Sandbox Reserved 1125: Difference between revisions

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MMP-8 is secreted as inactive proproteins and then activated after a cleavage by extracellular proteinases. Indeed, it can't be activated without removal of the activation peptide. After this protease activation, recent evidences suggest that, there is formation of an intramolecular complex between the Cysteine residue (Cys91) of the propeptide domain and essential zinc atom in the catalytic domain. It is called the ''Cysteine-switch'': it inhibits the action of MMP-8. This discovery is unprecedented in enzymology and offers the opportunity for multiple modes of physiological activation of MMP-8. Moreover, since conditions in different cells and tissues may match those necessary to effect one of these activation modes for a given MMP, this may offer metabolic flexibility in the control of MMP activation.<ref>PMID:2164689</ref>

To express collagenolytic activity, MMP-8 needs to have both the catalytic and hemopexin domains. The linker peptide can position the hemopexin domain in such a way that it bends over the active site of the catalytic domain. But understanding how the Hemopexin domain assists in the cleavage of collagen is elusive.<ref>PMID:15257288</ref> Thus, the collagen would be captured between these two domains. However, the active site cannot accommodate the entire triple helix in a native state. The linker peptide would, by means of its collagen-like conformation, change the quaternary structure of the captured collagen. Interactions between proline residues of the collagenase and a specific region of the collagen would generate a “proline zipper,” resulting in destabilization of the cleavage site area of the collagen. After destabilization, one chain of the triple helix fits in the specificity pocket or <scene name='71/719866/S1prime_pocket/1'>S1' pocket</scene> to the right of the active-site zinc. At first, the Gly residue of the substrate binds the <scene name='71/719866/Catalytic_site/4'>active site</scene> thanks to the Zn2+ atom. When it binds it takes the place of unstable water molecules and establishes stabilizing interactions with the active site thanks to its C terminal part.<ref>PMID:17185359</ref> The carboxyl group of the glutamate (GLU 198 in the green link above to the "active site" scene) serves as a general base to draw a proton from the displaced water molecule, thereby facilitating the nucleophilic attack of the water molecule on the carbonyl carbon of the peptide scissile bond. Then, the Alanine residue of the ~~enzyme~~ makes a hydrogen bond with the NH group of the substrate. Moreover, this NH group becomes the new N-terminus after cleavage.<ref name="inhibitor">PMID:12730128</ref>

To express collagenolytic activity, MMP-8 needs to have both the catalytic and hemopexin domains. The linker peptide can position the hemopexin domain in such a way that it bends over the active site of the catalytic domain. But understanding how the Hemopexin domain assists in the cleavage of collagen is elusive.<ref>PMID:15257288</ref> Thus, the collagen would be captured between these two domains. However, the active site cannot accommodate the entire triple helix in a native state. The linker peptide would, by means of its collagen-like conformation, change the quaternary structure of the captured collagen. Interactions between proline residues of the collagenase and a specific region of the collagen would generate a “proline zipper,” resulting in destabilization of the cleavage site area of the collagen. After destabilization, one chain of the triple helix fits in the specificity pocket or <scene name='71/719866/S1prime_pocket/1'>S1' pocket</scene> to the right of the active-site zinc. At first, the Gly residue of the substrate binds the <scene name='71/719866/Catalytic_site/4'>active site</scene> thanks to the Zn2+ atom. When it binds it takes the place of unstable water molecules and establishes stabilizing interactions with the active site thanks to its C terminal part.<ref>PMID:17185359</ref> The carboxyl group of the glutamate (GLU 198 in the green link above to the "active site" scene) serves as a general base to draw a proton from the displaced water molecule, thereby facilitating the nucleophilic attack of the water molecule on the carbonyl carbon of the peptide scissile bond. Then, the Alanine residue of the active site makes a hydrogen bond with the NH group of the substrate. Moreover, this NH group becomes the new N-terminus after cleavage.<ref name="inhibitor">PMID:12730128</ref>

The cleavage is at Gly775–Ile776 or Leu776 in each alpha-chain of the collagen molecule<ref name="hinge"/> and takes place at neutral pH. It generates fragments that spontaneously lose their helical conformation, denature to gelatin, and become soluble. The gelatin is then susceptible to attack by gelatinases and other proteases.<ref>[http://www.ebi.ac.uk/interpro/entry/IPR028709 "Neutrophil collagenase"]</ref>

Sandbox Reserved 1125: Difference between revisions

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 MMP-8 is secreted as inactive proproteins and then activated after a cleavage by extracellular proteinases. Indeed, it can't be activated without removal of the activation peptide. After this protease activation, recent evidences suggest that, there is formation of an intramolecular complex between the Cysteine residue (Cys91) of the propeptide domain and essential zinc atom in the catalytic domain. It is called the ''Cysteine-switch'': it inhibits the action of MMP-8. This discovery is unprecedented in enzymology and offers the opportunity for multiple modes of physiological activation of MMP-8. Moreover, since conditions in different cells and tissues may match those necessary to effect one of these activation modes for a given MMP, this may offer metabolic flexibility in the control of MMP activation.<ref>PMID:2164689</ref>
-To express collagenolytic activity, MMP-8 needs to have both the catalytic and hemopexin domains. The linker peptide can position the hemopexin domain in such a way that it bends over the active site of the catalytic domain. But understanding how the Hemopexin domain assists in the cleavage of collagen is elusive.<ref>PMID:15257288</ref> Thus, the collagen would be captured between these two domains. However, the active site cannot accommodate the entire triple helix in a native state. The linker peptide would, by means of its collagen-like conformation, change the quaternary structure of the captured collagen. Interactions between proline residues of the collagenase and a specific region of the collagen would generate a “proline zipper,” resulting in destabilization of the cleavage site area of the collagen. After destabilization, one chain of the triple helix fits in the specificity pocket or <scene name='71/719866/S1prime_pocket/1'>S1' pocket</scene> to the right of the active-site zinc. At first, the Gly residue of the substrate binds the <scene name='71/719866/Catalytic_site/4'>active site</scene> thanks to the Zn2+ atom. When it binds it takes the place of unstable water molecules and establishes stabilizing interactions with the active site thanks to its C terminal part.<ref>PMID:17185359</ref> The carboxyl group of the glutamate (GLU 198 in the green link above to the "active site" scene) serves as a general base to draw a proton from the displaced water molecule, thereby facilitating the nucleophilic attack of the water molecule on the carbonyl carbon of the peptide scissile bond. Then, the Alanine residue of the enzyme makes a hydrogen bond with the NH group of the substrate. Moreover, this NH group becomes the new N-terminus after cleavage.<ref name="inhibitor">PMID:12730128</ref>
+To express collagenolytic activity, MMP-8 needs to have both the catalytic and hemopexin domains. The linker peptide can position the hemopexin domain in such a way that it bends over the active site of the catalytic domain. But understanding how the Hemopexin domain assists in the cleavage of collagen is elusive.<ref>PMID:15257288</ref> Thus, the collagen would be captured between these two domains. However, the active site cannot accommodate the entire triple helix in a native state. The linker peptide would, by means of its collagen-like conformation, change the quaternary structure of the captured collagen. Interactions between proline residues of the collagenase and a specific region of the collagen would generate a “proline zipper,” resulting in destabilization of the cleavage site area of the collagen. After destabilization, one chain of the triple helix fits in the specificity pocket or <scene name='71/719866/S1prime_pocket/1'>S1' pocket</scene> to the right of the active-site zinc. At first, the Gly residue of the substrate binds the <scene name='71/719866/Catalytic_site/4'>active site</scene> thanks to the Zn2+ atom. When it binds it takes the place of unstable water molecules and establishes stabilizing interactions with the active site thanks to its C terminal part.<ref>PMID:17185359</ref> The carboxyl group of the glutamate (GLU 198 in the green link above to the "active site" scene) serves as a general base to draw a proton from the displaced water molecule, thereby facilitating the nucleophilic attack of the water molecule on the carbonyl carbon of the peptide scissile bond. Then, the Alanine residue of the active site makes a hydrogen bond with the NH group of the substrate. Moreover, this NH group becomes the new N-terminus after cleavage.<ref name="inhibitor">PMID:12730128</ref>
 The cleavage is at Gly775–Ile776 or Leu776 in each alpha-chain of the collagen molecule<ref name="hinge"/> and takes place at neutral pH. It generates fragments that spontaneously lose their helical conformation, denature to gelatin, and become soluble. The gelatin is then susceptible to attack by gelatinases and other proteases.<ref>[http://www.ebi.ac.uk/interpro/entry/IPR028709 "Neutrophil collagenase"]</ref>