Sandbox Reserved 818: Difference between revisions
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No specific receptors for PTX have been identified but many cell surface [http://en.wikipedia.org/wiki/Sialoglycoprotein '''sialoglycoproteins'''] are involved in the binding of PTX | No specific receptors for PTX have been identified but many cell surface [http://en.wikipedia.org/wiki/Sialoglycoprotein '''sialoglycoproteins'''] are involved in the binding of PTX | ||
<ref name="Peppler (1988)"> | <ref name="Peppler (1988)"> | ||
PMID:2454226 | |||
</ref> | </ref> | ||
, together with '''glycoproteins''': sugar moieties allow the recognition of the toxin and the carbohydrate sequence '''NeuAcα(2,6)-Galβ4GlcNAc''' is particularly important however sugar sequence alone is not sufficient | , together with '''glycoproteins''': sugar moieties allow the recognition of the toxin and the carbohydrate sequence '''NeuAcα(2,6)-Galβ4GlcNAc''' is particularly important however sugar sequence alone is not sufficient | ||
<ref name="Peppler (1988)"> | <ref name="Peppler (1988)"> | ||
PMID:3350815 | |||
</ref>. | </ref>. | ||
<br /> | <br /> | ||
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PTX binds its target cells through the ''B oligomer'' : ''S2'' and ''S3'' subunits contains at least two '''carbohydrate-binding sites''' | PTX binds its target cells through the ''B oligomer'' : ''S2'' and ''S3'' subunits contains at least two '''carbohydrate-binding sites''' | ||
<ref name="Read (1994)"> | <ref name="Read (1994)"> | ||
PMID:7634099 | |||
</ref> | </ref> | ||
. The N-terminal regions of these subunits are involved in receptor binding and the C-terminal domains of S2 and S3 adopt a fold found in other carbohydrate-binding proteins [73]. <br /> | . The N-terminal regions of these subunits are involved in receptor binding and the C-terminal domains of S2 and S3 adopt a fold found in other carbohydrate-binding proteins [73]. <br /> | ||
| Line 32: | Line 32: | ||
The B oligomer of PTX is involved in some biological activities of the toxin, independently of the enzyme activity. Thus <scene name='56/568016/Ptx_asn105/1'>Asn105</scene> in ''S2'' and <scene name='56/568016/Ptx_lys105/1'>Lys105</scene> in ''S3'' are important for the mitogenic activity of pertussis toxin on murine T lymphocytes | The B oligomer of PTX is involved in some biological activities of the toxin, independently of the enzyme activity. Thus <scene name='56/568016/Ptx_asn105/1'>Asn105</scene> in ''S2'' and <scene name='56/568016/Ptx_lys105/1'>Lys105</scene> in ''S3'' are important for the mitogenic activity of pertussis toxin on murine T lymphocytes | ||
<ref name="Locht93"> | <ref name="Locht93"> | ||
PMID:8418210 | |||
</ref> | </ref> | ||
, but not on human T cells | , but not on human T cells | ||
<ref name="Klein93"> | <ref name="Klein93"> | ||
PMID:8500874 | |||
</ref>. | </ref>. | ||
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After binding to the target cell receptors, PTX enters the cells via receptor mediated endocytosis, and then follows the ''retrograde transport system'', involving both the Golgi apparatus and the endoplasmic reticulum | After binding to the target cell receptors, PTX enters the cells via receptor mediated endocytosis, and then follows the ''retrograde transport system'', involving both the Golgi apparatus and the endoplasmic reticulum | ||
<ref name="Schmidt MA (1997)"> | <ref name="Schmidt MA (1997)"> | ||
PMID:9174670 | |||
</ref> | </ref> | ||
<ref name="Xu95"> | <ref name="Xu95"> | ||
PMID:7868253 | |||
</ref>. | </ref>. | ||
Electron microscopy studies have shown that PTX enters the cells via ''coated pits'' | Electron microscopy studies have shown that PTX enters the cells via ''coated pits'' | ||
<ref name="Schmidt MA (1997)"> | <ref name="Schmidt MA (1997)"> | ||
PMID:9174670 | |||
</ref>. | </ref>. | ||
But for now, PTX does not contain a clearly identified translocation domain in the B moiety. | But for now, PTX does not contain a clearly identified translocation domain in the B moiety. | ||
| Line 55: | Line 55: | ||
S1 is able to bind to phospholipids bilayers | S1 is able to bind to phospholipids bilayers | ||
<ref name="Carbonetti08"> | <ref name="Carbonetti08"> | ||
PMID:9174670 | |||
</ref> | </ref> | ||
, suggesting that it may directly interact with the target cell membranes and mediate its translocation, and also that the B oligomer is not essential for this step. Results obtained from cell transfection experiments support this hypothesis | , suggesting that it may directly interact with the target cell membranes and mediate its translocation, and also that the B oligomer is not essential for this step. Results obtained from cell transfection experiments support this hypothesis | ||
<ref name="Carbonetti01"> | <ref name="Carbonetti01"> | ||
PMID:11207619 | |||
</ref> | </ref> | ||
<ref name="Locht00"> | <ref name="Locht00"> | ||
PMID:11111919 | |||
</ref>. | </ref>. | ||
Binding of ATP to PTX | Binding of ATP to PTX | ||
<ref name="Read96"> | <ref name="Read96"> | ||
PMID:8637000 | |||
</ref> | </ref> | ||
destabilizes the S1–B oligomer interactions and results in the release of S1 from the holotoxin | destabilizes the S1–B oligomer interactions and results in the release of S1 from the holotoxin | ||
<ref name="Read97"> | <ref name="Read97"> | ||
PMID:9333321 | |||
</ref>. | </ref>. | ||
This was proposed to occur in the endoplasmic reticulum, as it contains ATP and [http://en.wikipedia.org/wiki/Protein_disulfide-isomerase disulfide isomerases], that may reduce the intramolecular disulphide bonds of S1, therefore help to release the subunit from the holotoxin | This was proposed to occur in the endoplasmic reticulum, as it contains ATP and [http://en.wikipedia.org/wiki/Protein_disulfide-isomerase disulfide isomerases], that may reduce the intramolecular disulphide bonds of S1, therefore help to release the subunit from the holotoxin | ||
<ref name="Hewlett83"> | <ref name="Hewlett83"> | ||
PMID:6311827 | |||
</ref>. | </ref>. | ||
| Line 90: | Line 90: | ||
The ADP-ribosylation of trimeric G proteins occurs on a '''cysteine residue''' in the ''C-terminal part of the α-subunit'' | The ADP-ribosylation of trimeric G proteins occurs on a '''cysteine residue''' in the ''C-terminal part of the α-subunit'' | ||
<ref name="Moss85"> | <ref name="Moss85"> | ||
PMID:3934172 | |||
</ref>. <br /> | </ref>. <br /> | ||
For that, the donor substrate used by PTX is '''NAD<sup>+</sup>''', which binds the toxin through <scene name='56/568016/Ptx_trp26/1'>Trp26</scene> | For that, the donor substrate used by PTX is '''NAD<sup>+</sup>''', which binds the toxin through <scene name='56/568016/Ptx_trp26/1'>Trp26</scene> | ||
<ref name="Barbieri89"> | <ref name="Barbieri89"> | ||
PMID:2551899 | |||
</ref> | </ref> | ||
<ref name="Feron89"> | <ref name="Feron89"> | ||
PMID:2470088 | |||
</ref> | </ref> | ||
, <scene name='56/568016/Ptx_arg9/1'>Arg9</scene> | , <scene name='56/568016/Ptx_arg9/1'>Arg9</scene> | ||
<ref name="Keith88"> | <ref name="Keith88"> | ||
PMID:2459776 | |||
</ref> | </ref> | ||
and <scene name='56/568016/Ptx_s1/2'>Cys41</scene> | and <scene name='56/568016/Ptx_s1/2'>Cys41</scene> | ||
<ref name="Keith90"> | <ref name="Keith90"> | ||
PMID:2155232 | |||
</ref> | </ref> | ||
located in the ''active site of S1''. <br /> | located in the ''active site of S1''. <br /> | ||
Concerning the acceptor substrate, it binds to the toxin through <scene name='56/568016/Ptx_180_219/1'>residues 180-219</scene> in the ''C-terminal region of S1'' | Concerning the acceptor substrate, it binds to the toxin through <scene name='56/568016/Ptx_180_219/1'>residues 180-219</scene> in the ''C-terminal region of S1'' | ||
<ref name="Barbieri91"> | <ref name="Barbieri91"> | ||
PMID:1748655 | |||
</ref>. | </ref>. | ||
These residues show indeed a high affinity for the G protein and are involved in the catalysis of the ADP-ribosylation | These residues show indeed a high affinity for the G protein and are involved in the catalysis of the ADP-ribosylation | ||
<ref name="Barbieri94"> | <ref name="Barbieri94"> | ||
PMID:8144593 | |||
</ref>. <br /> | </ref>. <br /> | ||
In the S1 subunit, the ''catalytic residues'' <scene name='56/568016/Ptx_his35/1'>His35</scene> | In the S1 subunit, the ''catalytic residues'' <scene name='56/568016/Ptx_his35/1'>His35</scene> | ||
<ref name="Locht94"> | <ref name="Locht94"> | ||
PMID:8119996 | |||
</ref> | </ref> | ||
<ref name="Barbieri94"> | <ref name="Barbieri94"> | ||
PMID:8144593 | |||
</ref> | </ref> | ||
and <scene name='56/568016/Ptx_glu129/1'>Glu129</scene> | and <scene name='56/568016/Ptx_glu129/1'>Glu129</scene> | ||
<ref name="Locht93"> | <ref name="Locht93"> | ||
PMID:7901213 | |||
</ref> | </ref> | ||
have been identified: His35 is involved in the ionization of the nucleophilic thiol of the cysteine residue in the G protein via its ε-N [99] and the carboxylate group of the Glu129 side chain is in contact with the 2'-ribo-hydroxyl of the NAD<sup>+</sup> | have been identified: His35 is involved in the ionization of the nucleophilic thiol of the cysteine residue in the G protein via its ε-N [99] and the carboxylate group of the Glu129 side chain is in contact with the 2'-ribo-hydroxyl of the NAD<sup>+</sup> | ||
<ref name="Antoine95"> | <ref name="Antoine95"> | ||
PMID:8527486 | |||
</ref>. | </ref>. | ||
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Cristal structure provided insight into the pathogenic mechanisms of PTX. Informations about the tertiary structure of the active site a good basis for elimination of the catalytic activity in recombinant molecules for vaccine use. | Cristal structure provided insight into the pathogenic mechanisms of PTX. Informations about the tertiary structure of the active site a good basis for elimination of the catalytic activity in recombinant molecules for vaccine use. | ||
For example, one highly detoxified PTX analog contains two alterations in the S1 subunit (Arg9 to Lys; Glu129 to Gly), each of which is able to totally abolish the enzymativ activity of the toxin. This molecule already belongs to the new-generation of pertussis vaccines <ref name="Karzon90"> | For example, one highly detoxified PTX analog contains two alterations in the S1 subunit (Arg9 to Lys; Glu129 to Gly), each of which is able to totally abolish the enzymativ activity of the toxin. This molecule already belongs to the new-generation of pertussis vaccines <ref name="Karzon90">PMID:2190139</ref>. | ||
</ref>. | |||