SB2013 L04gr5: Difference between revisions

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=Structure=

The lipoprotein, VlsE, consists of two invariable domains at the amino and carboxyl termini and a variable domain. When referring to the primary structure of the protein, the variable domain is a cassette region located between the two termini. The variable domain can be further broken down into variable regions (<scene name='SB2013_L04gr5/Variable_regions/3'>VRs</scene>) and invariable regions (<scene name='SB2013_L04gr5/Invariable_regions/2'>IRs</scene>) (Liang et al. 1999). When crystallized, VlsE forms a four molecule asymmetric unit (image of the unit) with each molecule having slight differences in their conformation. Although each molecule in the unit is slightly different, a single molecule of the protein consists of eleven [http://en.wikipedia.org/wiki/Alpha_helices α-helices] and four short [http://en.wikipedia.org/wiki/Beta_strand β-strands]. Helices α1 (aa 306-341), α2 (aa 68-87), α3 (aa 114-139), and α11 (aa 306-341) all form the <scene name='SB2013_L04gr5/Membrane_proximal_region/1'>membrane proximal region</scene> of VlsE while helices α4 through α10 form the primary region of the <scene name='SB2013_L04gr5/Membrane_distal_region/2'>membrane distal region</scene> of the protein. The four short β-strands each consist of 3 amino acids and can also be located in the membrane distal region. Covering the membrane distal part of VlsE are connecting loop regions, which lack any secondary structure and have different conformations in each of the molecules. (Eicken et al. 2002). The helices α3 through α10 form the invariable regions and are connected by the connecting loops which are classified as the variable regions. Although VlsE crystallizes into an asymmetrical unit, it appears primarily as monomeric in solution. Because the interface between VlsE molecules in the crystal structure buries approximately 13% of the accessible surface area of the monomers, Eicken et al.suggest that there is a possibility of VlsE existing as a [http://en.wikipedia.org/wiki/Protein_dimer dimer] when in its natural state (~~possible image~~).

The lipoprotein, VlsE, consists of two invariable domains at the amino and carboxyl termini and a variable domain (Figure 1). When referring to the primary structure of the protein, the variable domain is a cassette region located between the two termini. The variable domain can be further broken down into variable regions (<scene name='SB2013_L04gr5/Variable_regions/3'>VRs</scene>) and invariable regions (<scene name='SB2013_L04gr5/Invariable_regions/2'>IRs</scene>) (Liang et al. 1999). When crystallized, VlsE forms a four molecule asymmetric unit (image of the unit) with each molecule having slight differences in their conformation. Although each molecule in the unit is slightly different, a single molecule of the protein consists of eleven [http://en.wikipedia.org/wiki/Alpha_helices α-helices] and four short [http://en.wikipedia.org/wiki/Beta_strand β-strands]. Helices α1 (aa 306-341), α2 (aa 68-87), α3 (aa 114-139), and α11 (aa 306-341) all form the <scene name='SB2013_L04gr5/Membrane_proximal_region/1'>membrane proximal region</scene> of VlsE while helices α4 through α10 form the primary region of the <scene name='SB2013_L04gr5/Membrane_distal_region/2'>membrane distal region</scene> of the protein. The four short β-strands each consist of 3 amino acids and can also be located in the membrane distal region. Covering the membrane distal part of VlsE are connecting loop regions, which lack any secondary structure and have different conformations in each of the molecules. (Eicken et al. 2002). The helices α3 through α10 form the invariable regions and are connected by the connecting loops which are classified as the variable regions. Although VlsE crystallizes into an asymmetrical unit, it appears primarily as monomeric in solution. Because the interface between VlsE molecules in the crystal structure buries approximately 13% of the accessible surface area of the monomers, Eicken et al.suggest that there is a possibility of VlsE existing as a [http://en.wikipedia.org/wiki/Protein_dimer dimer] when in its natural state (Figure 2).

[[Image:~~Dimerized~~ VlsE.jpg]]

[[Image:VlsE 2-d image.jpg]]

Figure 1 shows the different domains of VlsE.

<scene name='SB2013_L04gr5/Reset_button/1'>Reset</scene>

~~[[Image:VlsE 2-d image.jpg]]~~

[[Image:Dimerized VlsE.jpg]]

Figure 2 shows the possible dimerization of VlsE.

=Antigenic Variation=

Antigenic variation is the process through which an organism is able to evade its host’s immune system. The antigenic variation that occurs in VlsE uses a complex genetic conversion mechanism that is seen to be concentrated in the VRs. The complex genetic system for VlsE is located near the right telomere on a 28-kb linear plasmid (lp28-1) in strains of B. burgdorferi. This [http://en.wikipedia.org/wiki/Locus_%28genetics%29 locus] has been shown to be a crucial element for the persistence and virulence of Lyme disease (Bankhead and Chaconas 2007). The vls antigenic variation locus consists of a vls expression site (vlsE) and 15 silent vls cassettes that reside just upstream of the site. The vlsE cassette region, which is the variable domain and doesn’t include the invariable amino or carboxyl termini, has approximately 92% DNA sequence identity with the silent vls cassettes. However, the silent vls cassettes lack promoter sequences and are therefore not expressed. Throughout the course of infection, the sequences for the flanking termini and the silent vls cassettes are conserved while the vlsE sequence is recombined. This suggests that the genetic variation mechanism occurs by copying segments of the 15 silent vls cassettes and completely replacing corresponding segments of vlsE sequences. The resulting differences are centralized in the highly variable regions of the vls cassettes. This allows for the constant evolution of the VR structures and evades the antibodies of the host immune system (Zhang and Norris 1998).

SB2013 L04gr5: Difference between revisions

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 <Structure load='1L8W' size='400' frame='true' align='right' caption='Crystallized Structure of VlsE' scene='' />
 =Structure=
-The lipoprotein, VlsE, consists of two invariable domains at the amino and carboxyl termini and a variable domain.  When referring to the primary structure of the protein, the variable domain is a cassette region located between the two termini.  The variable domain can be further broken down into variable regions (<scene name='SB2013_L04gr5/Variable_regions/3'>VRs</scene>) and invariable regions (<scene name='SB2013_L04gr5/Invariable_regions/2'>IRs</scene>) (Liang et al. 1999).  When crystallized, VlsE forms a four molecule asymmetric unit (image of the unit) with each molecule having slight differences in their conformation.  Although each molecule in the unit is slightly different, a single molecule of the protein consists of eleven [http://en.wikipedia.org/wiki/Alpha_helices α-helices] and four short [http://en.wikipedia.org/wiki/Beta_strand β-strands].  Helices α1 (aa 306-341), α2 (aa 68-87), α3 (aa 114-139), and α11 (aa 306-341) all form the <scene name='SB2013_L04gr5/Membrane_proximal_region/1'>membrane proximal region</scene> of VlsE while helices α4 through α10 form the primary region of the <scene name='SB2013_L04gr5/Membrane_distal_region/2'>membrane distal region</scene> of the protein.  The four short β-strands each consist of 3 amino acids and can also be located in the membrane distal region.  Covering the membrane distal part of VlsE are connecting loop regions, which lack any secondary structure and have different conformations in each of the molecules. (Eicken et al. 2002).  The helices α3 through α10 form the invariable regions and are connected by the connecting loops which are classified as the variable regions.  Although VlsE crystallizes into an asymmetrical unit, it appears primarily as monomeric in solution.  Because the interface between VlsE molecules in the crystal structure buries approximately 13% of the accessible surface area of the monomers, Eicken et al.suggest that there is a possibility of VlsE existing as a [http://en.wikipedia.org/wiki/Protein_dimer dimer] when in its natural state (possible image).
+The lipoprotein, VlsE, consists of two invariable domains at the amino and carboxyl termini and a variable domain (Figure 1).  When referring to the primary structure of the protein, the variable domain is a cassette region located between the two termini.  The variable domain can be further broken down into variable regions (<scene name='SB2013_L04gr5/Variable_regions/3'>VRs</scene>) and invariable regions (<scene name='SB2013_L04gr5/Invariable_regions/2'>IRs</scene>) (Liang et al. 1999).  When crystallized, VlsE forms a four molecule asymmetric unit (image of the unit) with each molecule having slight differences in their conformation.  Although each molecule in the unit is slightly different, a single molecule of the protein consists of eleven [http://en.wikipedia.org/wiki/Alpha_helices α-helices] and four short [http://en.wikipedia.org/wiki/Beta_strand β-strands].  Helices α1 (aa 306-341), α2 (aa 68-87), α3 (aa 114-139), and α11 (aa 306-341) all form the <scene name='SB2013_L04gr5/Membrane_proximal_region/1'>membrane proximal region</scene> of VlsE while helices α4 through α10 form the primary region of the <scene name='SB2013_L04gr5/Membrane_distal_region/2'>membrane distal region</scene> of the protein.  The four short β-strands each consist of 3 amino acids and can also be located in the membrane distal region.  Covering the membrane distal part of VlsE are connecting loop regions, which lack any secondary structure and have different conformations in each of the molecules. (Eicken et al. 2002).  The helices α3 through α10 form the invariable regions and are connected by the connecting loops which are classified as the variable regions.  Although VlsE crystallizes into an asymmetrical unit, it appears primarily as monomeric in solution.  Because the interface between VlsE molecules in the crystal structure buries approximately 13% of the accessible surface area of the monomers, Eicken et al.suggest that there is a possibility of VlsE existing as a [http://en.wikipedia.org/wiki/Protein_dimer dimer] when in its natural state (Figure 2).
-[[Image:Dimerized VlsE.jpg]]
+[[Image:VlsE 2-d image.jpg]]
+Figure 1 shows the different domains of VlsE.
 <scene name='SB2013_L04gr5/Reset_button/1'>Reset</scene>
-[[Image:VlsE 2-d image.jpg]]
+[[Image:Dimerized VlsE.jpg]]
+Figure 2 shows the possible dimerization of VlsE.
 =Antigenic Variation=
 Antigenic variation is the process through which an organism is able to evade its host’s immune system.  The antigenic variation that occurs in VlsE uses a complex genetic conversion mechanism that is seen to be concentrated in the VRs. The complex genetic system for VlsE is located near the right telomere on a 28-kb linear plasmid (lp28-1) in strains of B. burgdorferi.  This [http://en.wikipedia.org/wiki/Locus_%28genetics%29 locus] has been shown to be a crucial element for the persistence and virulence of Lyme disease (Bankhead and Chaconas 2007).  The vls antigenic variation locus consists of a vls expression site (vlsE) and 15 silent vls cassettes that reside just upstream of the site.  The vlsE cassette region, which is the variable domain and doesn’t include the invariable amino or carboxyl termini, has approximately 92% DNA sequence identity with the silent vls cassettes.  However, the silent vls cassettes lack promoter sequences and are therefore not expressed.  Throughout the course of infection, the sequences for the flanking termini and the silent vls cassettes are conserved while the vlsE sequence is recombined.  This suggests that the genetic variation mechanism occurs by copying segments of the 15 silent vls cassettes and completely replacing corresponding segments of vlsE sequences.  The resulting differences are centralized in the highly variable regions of the vls cassettes.  This allows for the constant evolution of the VR structures and evades the antibodies of the host immune system (Zhang and Norris 1998).