Proteopedia - User contributions [en]

ToxT

2011-11-29T23:59:45Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera] Rehydration is sufficient as treatment.
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA (specific promoters for virulence genes).<ref name="structure">PMID: 20133655</ref>[http://www.pnas.org/content/107/7/2860/F3.large.jpg]. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is made from several residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.large.jpg]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate (PAM) appears to change ToxT's conformation, and thus lower its ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. PAM brings K31 and K230 together from either end of the protein, and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes helix six to be pulled into an unfavorable conformation that deters DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, PAM is in lower concentration and tends subsequently not to be bound, and the two lysine residues repel each other to give ToxT an open conformation. The freedom of helices six and seven to find a favorable configuration allows DNA binding to occur.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is shown, which can be bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T23:56:36Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera] Rehydration is sufficient as treatment.
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA (specific promoters for virulence genes).<ref name="structure">PMID: 20133655</ref>[http://www.pnas.org/content/107/7/2860/F3.large.jpg]. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is made from several residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.large.jpg]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate (PAM) appears to change ToxT's conformation, and thus lower its ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. PAM brings K31 and K230 together from either end of the protein, and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes helix six to be pulled into an unfavorable conformation that deters DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, PAM is in lower concentration and tends subsequently not to be bound, and the two lysine residues repel each other to give ToxT an open conformation. The freedom of helices six and seven to find a favorable configuration allows DNA binding to occur.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is shown, which can be bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T23:46:48Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA (specific promoters for virulence genes).<ref name="structure">PMID: 20133655</ref>[http://www.pnas.org/content/107/7/2860/F3.large.jpg]. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is made from several residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.large.jpg]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate (PAM) appears to change ToxT's conformation, and thus lower its ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. PAM brings K31 and K230 together from either end of the protein, and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes helix six to be pulled into an unfavorable conformation that deters DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, PAM is in lower concentration and tends subsequently not to be bound, and the two lysine residues repel each other to give ToxT an open conformation. The freedom of helices six and seven to find a favorable configuration allows DNA binding to occur.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is shown, which can be bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T23:41:20Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA (specific promoters for virulence genes).<ref name="structure">PMID: 20133655</ref>[http://www.pnas.org/content/107/7/2860/F3.large.jpg]. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is made from several residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.large.jpg]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate (PAM) appears to change ToxT's conformation, and thus lower its ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. PAM brings K31 and K230 together from either end of the protein, and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes helix six to be pulled into an unfavorable conformation that deters DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, PAM is in lower concentration and tends subsequently not to be bound, and the two lysine residues repel each other to give ToxT an open conformation. The freedom of helices six and seven to find a favorable configuration allows DNA binding to occur.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T23:40:01Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA (specific promoters for virulence genes).<ref name="structure">PMID: 20133655</ref>[http://www.pnas.org/content/107/7/2860/F3.large.jpg]. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is made from several residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.large.jpg]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate (PAM) appears to change ToxT's conformation, and thus lower its ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. PAM brings K31 and K230 together from either end of the protein, and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, PAM is in lower concentration and tends subsequently not to be bound, and the two lysine residues repel each other to give ToxT an open conformation. The freedom of helices six and seven to find a favorable configuration allows DNA binding to occur.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T23:30:21Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA (specific promoters for virulence genes).<ref name="structure">PMID: 20133655</ref>[http://www.pnas.org/content/107/7/2860/F3.large.jpg]. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is made from several residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.large.jpg]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate (PAM) appears change ToxT's conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. PAM brings K31 and K230 together from either end of the protein, and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, PAM is in lower concentration and tends subsequently not to be bound, and the two lysine residues repel each other to give ToxT an open conformation. The freedom of helices six and seven to find a favorable configuration allows DNA binding to occur.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T23:02:07Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>[http://www.pnas.org/content/107/7/2860/F3.large.jpg]. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is made from several residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.large.jpg]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate (PAM) appears change ToxT's conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. PAM brings K31 and K230 together from either end of the protein, and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, PAM is in lower concentration and tends subsequently not to be bound, and the two lysine residues repel each other to give ToxT an open conformation. The freedom of helices six and seven to find a favorable configuration allows DNA binding to occur.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T23:00:54Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>[http://www.pnas.org/content/107/7/2860/F3.large.jpg]. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is made from several residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.large.jpg]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate (PAM) appears change ToxT's conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. PAM brings K31 and K230 together from either end of the protein, and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, PAM is not bound, and the two lysine residues repel each other to give ToxT an open conformation. The freedom of helix six and seven to find a favorable configuration allows DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T22:56:05Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>[http://www.pnas.org/content/107/7/2860/F3.large.jpg]. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is made from several residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.large.jpg]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T22:53:14Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>[http://www.pnas.org/content/107/7/2860/F3.large.jpg]. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is made from several residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.expansion.html]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T22:49:34Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>[http://www.pnas.org/content/107/7/2860/F3.large.jpg]. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is largely made up of residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.expansion.html]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T22:45:32Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is largely made up of residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.expansion.html]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (as discussed above). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T22:22:21Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='structure' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Other Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is largely made up of residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.expansion.html]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T22:17:35Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Other Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (one on either side of the black linker). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is largely made up of residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.expansion.html]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T22:12:49Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Other Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (helix in blue, turn in teal). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is composed of seven alpha helices, and is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is largely made up of residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230 (for detail, see Figure 1B of: [http://www.pnas.org/content/107/7/2860/F1.expansion.html]). This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T20:27:01Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Other Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (helix in blue, turn in teal). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is composed of seven alpha helices, and is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is largely made up of residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230. This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, perpetuating the infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T20:25:36Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. ToxT is a cytoplasmic protein that is activated in turn by ToxR, which is itself activated by ToxS in response to environmental stimuli.<ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref> These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Other Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (helix in blue, turn in teal). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is composed of seven alpha helices, and is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is largely made up of residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230. This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, resulting in an infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T18:45:35Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Other Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (helix in blue, turn in teal). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is composed of seven alpha helices, and is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is largely made up of residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230. This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, resulting in an infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Date of access: 2011-11-28.</ref>
==References==
<references/>

ToxT

2011-11-29T18:44:54Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Other Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (helix in blue, turn in teal). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is composed of seven alpha helices, and is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is largely made up of residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230. This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, resulting in an infection. <ref>Kenneth Todar [http://www.textbookofbacteriology.net/cholera.html] ''Vibrio cholerae'' and Asiatic Cholera, Todar's Online Textbook of Bacteriology. Accessdate=2011-11-29.</ref>
==References==
<references/>

ToxT

2011-11-29T18:40:24Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Other Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (helix in blue, turn in teal). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is composed of seven alpha helices, and is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is largely made up of residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230. This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
</StructureSection>
==Further Study==
Conclusive results about what activates ToxT itself has not yet been found. The varying activity of ToxT dependent on the presence of cis-palmitoleate or other unsaturated fatty acids represents a detailed method of effective pathogenicity in humans, but may not be a reasonable target for drug treatment. By restricting transcription (and thus translation and protein production) of virulence genes until the bacterium is determined to be in a favorable location for infection, Vibrio cholerae avoids wasting energy producing virulence factors that will just be cleared by the intestine. This is a specific mechanism to ensure that the bacterium also injects CT and TCP where they will do the most damage, resulting in an infection. <ref>{{cite web|first=Kenneth |last=Todar |url=http://www.textbookofbacteriology.net/cholera.html |title=''Vibrio cholerae'' and Asiatic Cholera |publisher=Todar's Online Textbook of Bacteriology |date= |accessdate=2011-11-29}}</ref>
==References==
<references/>

ToxT

2011-11-29T18:20:38Z

Ingrid Youngworth:

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]
<StructureSection load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' >
==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Other Structural Features==
DNA-binding. ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (helix in blue, turn in teal). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is composed of seven alpha helices, and is located at the C-terminus.<ref name="structure">PMID: 20133655</ref> Assuming ToxT is similar in mechanism to other AraC proteins, helix six from HTH1 and helix nine from HTH2 become aligned with the help of helix seven (the polar linking region) to allow binding to major consecutive grooves of target DNA.<ref name="structure">PMID: 20133655</ref>. The conformation of helix seven is dependent on the ligand bound.
 
 
Ligand-binding. <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> or "jelly-roll" with three other alpha helices (overall making up the <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/N-terminus/1'>N-terminus</scene>) contain a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/1'>binding pocket</scene>. This is largely made up of residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.<ref name="structure">PMID: 20133655</ref> This pocket contains a ligand: <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Binding_pocket/2'>cis-palmitoleate</scene> <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Salt_bridges_pam/1'>salt bridges</scene> with residues K31 and K230. This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT. The
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref> The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. Here, binding of PAM brings K31 and K230 together and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes pulling helix six into an unfavorable conformation that disallows DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, the two lysine residues repel each other and give ToxT an open conformation by giving helix seven and thus six freedom, allowing DNA binding.<ref name="structure">PMID: 20133655</ref>
 
 
Dimerization. Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer.<ref name="dimerization">PMID: 21415495
</ref> The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
</StructureSection>
==References==
<references/>

ToxT

2011-11-29T17:03:03Z

Ingrid Youngworth:

ToxT

2011-11-29T17:01:12Z

Ingrid Youngworth:

ToxT

2011-11-29T16:50:07Z

Ingrid Youngworth:

ToxT

2011-11-29T16:48:02Z

Ingrid Youngworth:

ToxT

2011-11-29T16:46:35Z

Ingrid Youngworth:

ToxT

2011-11-29T16:37:51Z

Ingrid Youngworth:

ToxT

2011-11-29T16:25:48Z

Ingrid Youngworth:

ToxT

2011-11-29T16:25:16Z

Ingrid Youngworth:

ToxT

2011-11-29T16:22:04Z

Ingrid Youngworth:

ToxT

2011-11-29T16:20:40Z

Ingrid Youngworth:

ToxT

2011-11-29T16:18:02Z

Ingrid Youngworth:

ToxT

2011-11-29T16:17:27Z

Ingrid Youngworth:

ToxT

2011-11-29T16:16:52Z

Ingrid Youngworth:

ToxT

2011-11-29T16:03:01Z

Ingrid Youngworth:

ToxT

2011-11-29T15:48:18Z

Ingrid Youngworth:

ToxT

2011-11-29T15:44:51Z

Ingrid Youngworth:

<Structure load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' />

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://en.wikipedia.org/wiki/Cholera]

==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Other Structural Features==
ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (helix in blue, turn in teal). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is composed of seven alpha helices.<ref name="structure">PMID: 20133655</ref>
 
 
<scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> contains a binding pocket that contains a ligand: cis-palmitoleate, <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. This unsaturated fatty acid, like other UFAs,[http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref>
 
 
Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer. The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==References==
<references/>

ToxT

2011-11-27T23:06:49Z

Ingrid Youngworth:

<Structure load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' />

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://http://en.wikipedia.org/wiki/Cholera]

==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Other Structural Features==
ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Two_hth_domains/1'>DNA-binding domain</scene> with two helix-turn-helix motifs (helix in blue, turn in teal). <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix (shown in black). The overall domain is composed of seven alpha helices.<ref name="structure">PMID: 20133655</ref>
 
 
<scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> contains a binding pocket that contains a ligand: cis-palmitoleate, <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. This unsaturated fatty acid, like other UFAs,[http://http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref>
 
 
Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer. The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==References==
<references/>

ToxT

2011-11-27T22:54:26Z

Ingrid Youngworth: /* Ligand */

<Structure load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' />

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://http://en.wikipedia.org/wiki/Cholera]

==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Structural Features==
ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a DNA-binding domain with two helix-turn-helix motifs. <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix. The overall domain is composed of seven alpha helices.<ref name="structure">PMID: 20133655</ref>
 
 
<scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> contains a binding pocket that contains a ligand: cis-palmitoleate, <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. This unsaturated fatty acid, like other UFAs,[http://http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref>
 
 
Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer. The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==References==
<references/>

ToxT

2011-11-27T22:51:24Z

Ingrid Youngworth:

<Structure load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' />

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://http://en.wikipedia.org/wiki/Cholera]

==Ligand==
In this resolved structure, <scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Pam/2'>cis-palmitoleate</scene>[http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=3gbg&template=ligands.html&l=1.1] is present and bound in the beta sheet barrel (further discussed below). This unsaturated fatty acid reduces virulence expression in Vibrio cholerae.

==Structural Features==
ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a DNA-binding domain with two helix-turn-helix motifs. <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix. The overall domain is composed of seven alpha helices.<ref name="structure">PMID: 20133655</ref>
 
 
<scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> contains a binding pocket that contains a ligand: cis-palmitoleate, <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. This unsaturated fatty acid, like other UFAs,[http://http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref>
 
 
Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer. The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==References==
<references/>

ToxT

2011-11-27T22:37:32Z

Ingrid Youngworth:

<Structure load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' />

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://http://en.wikipedia.org/wiki/Cholera]
==Structural Features==
ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a DNA-binding domain with two helix-turn-helix motifs. <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix. The overall domain is composed of seven alpha helices.<ref name="structure">PMID: 20133655</ref>
 
 
<scene name='ToxT_Transcriptional_Regulator_in_Vibrio_cholerae/Barrel/1'>A nine-stranded beta sheet sandwich</scene> contains a binding pocket that contains a ligand: cis-palmitoleate, <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. This unsaturated fatty acid, like other UFAs,[http://http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref>
 
 
Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer. The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==References==
<references/>

ToxT

2011-11-27T21:58:56Z

Ingrid Youngworth:

<Structure load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' />

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://http://en.wikipedia.org/wiki/Cholera]
==Structural Features==
ToxT belongs to a family of transcriptional regulators headed by and known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a DNA-binding domain with two helix-turn-helix motifs. <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix. The overall domain is composed of seven alpha helices.<ref name="structure">PMID: 20133655</ref>
 
 
A nine-stranded beta sheet sandwich contains a binding pocket that contains a ligand: cis-palmitoleate, <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. This unsaturated fatty acid, like other UFAs,[http://http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref>
 
 
Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer. The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==References==
<references/>

ToxT

2011-11-27T00:27:22Z

Ingrid Youngworth:

<Structure load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' />

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://http://en.wikipedia.org/wiki/Cholera]
==Structural Features==
ToxT belongs to a family of transcriptional regulators known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is characterized by a 100 amino acid region of sequence similarity that forms a DNA-binding domain with two helix-turn-helix motifs. <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix. The overall domain is composed of seven alpha helices.<ref name="structure">PMID: 20133655</ref>
 
 
A nine-stranded beta sheet sandwich contains a binding pocket that contains a ligand: cis-palmitoleate, <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. This unsaturated fatty acid, like other UFAs,[http://http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref>
 
 
Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer. The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==References==
<references/>

ToxT

2011-11-27T00:26:39Z

Ingrid Youngworth:

<Structure load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' />

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://http://en.wikipedia.org/wiki/Cholera]
==Structural Features==
ToxT belongs to a family of transcriptional regulators known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is defined by a 100 amino acid region of sequence similarity that forms a DNA-binding domain with two helix-turn-helix motifs. <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by a very polar alpha helix. The overall domain is composed of seven alpha helices.<ref name="structure">PMID: 20133655</ref>
 
 
A nine-stranded beta sheet sandwich contains a binding pocket that contains a ligand: cis-palmitoleate, <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. This unsaturated fatty acid, like other UFAs,[http://http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref>
 
 
Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer. The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form.<ref name="virstatin">PMID:17283330</ref>ToxT binds to thirteen base pair sequences (can be single, direct, or inverted repeats) called toxboxes in order to activate their respective promoters.[http://www.sigwiki.info/wiki/Signature:ToxBox]
==References==
<references/>

ToxT

2011-11-27T00:17:13Z

Ingrid Youngworth:

<Structure load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' />

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://http://en.wikipedia.org/wiki/Cholera]
==Structural Features==
ToxT belongs to a family of transcriptional regulators known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is defined by a 100 amino acid region of sequence similarity that forms a DNA-binding domain with two helix-turn-helix motifs. <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by another alpha helix, which is very polar.
 
 
A nine-stranded beta sheet sandwich contains a binding pocket that contains a ligand: cis-palmitoleate, <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. This unsaturated fatty acid, like other UFAs,[http://http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref>
 
 
Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer. The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form. <ref name="virstatin">PMID:17283330</ref>

==References==
<references/>

ToxT

2011-11-27T00:16:48Z

Ingrid Youngworth:

<Structure load='3gbg' color='cpk' size='500' frame='true' align='right' caption='ToxT, 1.9 Angstrom resolution crystal structure' />

The crystal structure of ToxT is resolved in monomeric form, after isolation from Vibrio cholerae strain O395.<ref name="structure">PMID: 20133655</ref>
==Introduction==
ToxT is a molecule at the end of a transcriptional cascade that autoregulates the transcription of the primary virulence factors of Vibrio cholerae[http://http://en.wikipedia.org/wiki/Vibrio_cholerae] and itself. These two factors, cholera toxin (CT)[http://http://en.wikipedia.org/wiki/Cholera_toxin] and the toxin co-regulated pilus (TCP), are instrumental in causing the disease cholera[http://http://en.wikipedia.org/wiki/Cholera]. This is an intestinal infection resulting in massive water loss in the affected individual, causing extreme dehydration.[http://http://en.wikipedia.org/wiki/Cholera]
==Structural Features==
ToxT belongs to a family of transcriptional regulators known as AraC.<ref name="structure">PMID: 20133655</ref> The AraC family is defined by a 100 amino acid region of sequence similarity that forms a DNA-binding domain with two helix-turn-helix motifs. <ref name="arac">PMID: 11282467</ref> The two HTH regions are linked by another alpha helix, which is very polar.
 
 
A nine-stranded beta sheet sandwich contains a binding pocket that contains a ligand: cis-palmitoleate, <ref name="structure">PMID: 20133655</ref> which appears to have a negative effect on virulence when present in vitro. This unsaturated fatty acid, like other UFAs,[http://http://en.wikipedia.org/wiki/Fatty_acid#Unsaturated_fatty_acids] tend to inhibit genes under the control of ToxT.
Specifically, the cis-palmitoleate appears to bind directly to ToxT, change its conformation, and thus lower the ability to bind DNA and form dimers.<ref name="structure">PMID: 20133655</ref>
 
 
Though the structure shown is a monomer with two overall domains (N-terminal and C-terminal), ToxT tends to form a dimer. The preferred state of ToxT varies between promoters, but binding to the ctx promoter to generate cholera toxin appears to be possible only in the dimer form. <ref name="virstatin">PMID:17283330</ref>

==References==
<references/>

ToxT

2011-11-27T00:12:03Z

Ingrid Youngworth:

ToxT

2011-11-27T00:00:16Z

Ingrid Youngworth:

ToxT

2011-11-26T23:59:48Z

Ingrid Youngworth:

ToxT

2011-11-26T23:58:20Z

Ingrid Youngworth: