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==General structure==
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==Structure==
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Serpins are a superfamily of functionally distinct but structurally conserved proteins. <ref>JBC Papers in Press. Published on July 2, 2001 as Manuscript R100016200 THE SERPINS ARE AN EXPANDING SUPERFAMILY OF
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===Generals===
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Serpins are a superfamily of proteins wich are functionally distinct but structurally conserved. <ref>JBC Papers in Press. Published on July 2, 2001 as Manuscript R100016200 THE SERPINS ARE AN EXPANDING SUPERFAMILY OF
STRUCTURALLY SIMILAR BUT FUNCTIONALLY DIVERSE PROTEINShttp://www.jbc.org/content/early/2001/07/02/jbc.R100016200.full.pdf DOI : 2001/07/02/jbc.R100016200.full.pdf </ref>
STRUCTURALLY SIMILAR BUT FUNCTIONALLY DIVERSE PROTEINShttp://www.jbc.org/content/early/2001/07/02/jbc.R100016200.full.pdf DOI : 2001/07/02/jbc.R100016200.full.pdf </ref>
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SerpinB3 means serin protease inhibitor, clade B (ovalbumin), member 3. The particularity of Serpin B3 is to target proteases wich have a nucleophilic cysteine instead of serine in their catalytic site.
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SerpinB3 means serin protease inhibitor, clade B (for ovalbumin), member 3. The particularity of Serpin B3 is to target proteases which have a nucleophilic cysteine instead of serine in their catalytic site.
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SCCA1 is a <scene name='60/604473/Trimeric/1'>trimeric protein</scene><ref> PMID : 19166818 </ref>
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SCCA1 is a <scene name='60/604473/Trimeric/1'>trimeric protein</scene><ref> PMID : 19166818 </ref>. <scene name='60/604473/One_subunit/1'>one subunit</scene> has three β sheets termed <scene name='60/604473/A_beta_sheet/3'>A (7 stranded)</scene>, <scene name='60/604473/B_beta_sheet/2'>B (5 stranded)</scene> and <scene name='60/604473/C_beta_sheet/2'>C (6 stranded)</scene> and <scene name='60/604473/Alpha_helices/1'>11 α helices (hA to hK)</scene> <ref>Gary A. Silverman1*, Phillip I. Bird2
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. Like all for serpins, <scene name='60/604473/One_subunit/1'>one subunit</scene> has three β sheets termed <scene name='60/604473/A_beta_sheet/3'>A (7 stranded)</scene>, <scene name='60/604473/B_beta_sheet/2'>B (5 stranded)</scene> and <scene name='60/604473/C_beta_sheet/2'>C (6 stranded)</scene> and <scene name='60/604473/Alpha_helices/1'>11 α helices (hA to hK)</scene> <ref>Gary A. Silverman1*, Phillip I. Bird2
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, Robin W. Carrell3
, Robin W. Carrell3
, Frank C. Church4
, Frank C. Church4
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, Eileen RemoldO'Donnell9
, Eileen RemoldO'Donnell9
, Guy S. Salvesen10, James Travis11 and James C. Whisstock, THE SERPINS ARE AN EXPANDING SUPERFAMILY OF
, Guy S. Salvesen10, James Travis11 and James C. Whisstock, THE SERPINS ARE AN EXPANDING SUPERFAMILY OF
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STRUCTURALLY SIMILAR BUT FUNCTIONALLY DIVERSE PROTEINS, http://www.jbc.org/content/early/2001/07/02/jbc.R100016200.full.pdf DOI : 2001/07/02/jbc.R100016200.full.pdf </ref> <ref>PDB, Crystal structure of human squamous cell carcinoma antigen 1 http://www.rcsb.org/pdb/explore/remediatedSequence.do?structureId=2ZV6&bionumber=1 DOI : pdb/explore/remediatedSequence.do?structureId=2ZV6&bionumber=1</ref> .
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STRUCTURALLY SIMILAR BUT FUNCTIONALLY DIVERSE PROTEINS, http://www.jbc.org/content/early/2001/07/02/jbc.R100016200.full.pdf DOI : 2001/07/02/jbc.R100016200.full.pdf </ref> <ref>PDB, Crystal structure of human squamous cell carcinoma antigen 1 http://www.rcsb.org/pdb/explore/remediatedSequence.do?structureId=2ZV6&bionumber=1 DOI : pdb/explore/remediatedSequence.do?structureId=2ZV6&bionumber=1</ref>.
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The most important part of Serpins is an exposed region of 20 amino acids near the C terminus named the reactive center loop (<scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene>). The amino-acids of <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> are very conservated for Serpin B3 and allow the specificity interaction of the inhibitor for the target protease<ref> PMID : PMC24842</ref>.
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The most important domain of SCCA1 is an exposed region of 20 amino acids near the C terminus named the reactive center loop (<scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene>). The amino-acids of <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> are very conservated for SCCA1 and allow the specificity interaction between the inhibitor and the target protease<ref> PMID : PMC24842</ref>.
===Conformational changes of serpins===
===Conformational changes of serpins===
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Structural studies on serpins revealed that inhibitory members of the family undergo an unusual conformational change, termed the Stressed to Relaxed (S to R) transition. During this structural transition the <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> inserts into <scene name='60/604473/A_beta_sheet/3'>A β-sheet</scene> and forms an extra fourth β strand . The serpin conformational change is key to the mechanism of inhibition of target proteases. <scene name='60/604473/Rcl_insertion_into_beta_sheet/1'>Some amino-acids of RCL</scene> wich belong to a consensus sequence for inhibitory serpins are thought to permit efficient and rapid insertion of the <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> into the <scene name='60/604473/A_beta_sheet/3'>A β-sheet</scene>.<ref> James C Whisstocka, 2, Richard Skinnera, 2, Robin W Carrella, Arthur M Leska, Conformational changes in serpins: I. the native and cleaved conformations of α1-antitrypsin1, http://www.sciencedirect.com/science/article/pii/S0022283699935209 DOI:pii/S0022283699935209</ref>
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The inhibitory members of serpin family undergo an unusual conformational change, the Stressed to Relaxed transition. This structural transition causes the <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> insertion into <scene name='60/604473/A_beta_sheet/3'>A β-sheet</scene> thereby the <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> forms an extra β strand . The serpin conformational change is essential for the inhibition mechanism of proteases. <scene name='60/604473/Rcl_insertion_into_beta_sheet/1'>Some amino-acids of RCL</scene> wich belong to a consensus sequence for inhibitory serpins are thought to permit the insertion of the <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> into the <scene name='60/604473/A_beta_sheet/3'>A β-sheet</scene>.<ref> James C Whisstocka, 2, Richard Skinnera, 2, Robin W Carrella, Arthur M Leska, Conformational changes in serpins: I. the native and cleaved conformations of α1-antitrypsin1, http://www.sciencedirect.com/science/article/pii/S0022283699935209 DOI:pii/S0022283699935209</ref>
[[Image:Structure region.jpg|300px]] [[Image:Fontion3.jpg|400px]]
[[Image:Structure region.jpg|300px]] [[Image:Fontion3.jpg|400px]]
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===Cysteine proteases mecanism===
===Cysteine proteases mecanism===
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When attacking a substrate, proteases catalyze peptide bond cleavage in a two-step process. Initially, the catalytic cysteine performs a nucleophilic attack on the peptide bond of the substrate. This releases the new N-terminus and forms an new bond between the enzyme and the substrate. This covalent enzyme-substrate complex is called an acyl enzyme intermediate. Subsequent to this, this bond is hydrolysed and the new C-terminus is released.
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When a cystein protease attacks a substrate, the peptide bond cleavage is catalyzed. Firstly, the catalytic cysteine performs a nucleophilic attack on the substrate peptide bond. Thus the new N-terminusis is released and a new bond between the enzyme and the substrate is created forming a covalent enzyme-substrate complex called the acyl enzyme intermediate. Finally, this new bond is hydrolysed and the new C-terminus is released.
http://en.wikipedia.org/wiki/Serpin
http://en.wikipedia.org/wiki/Serpin
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===Protease inhibition===
===Protease inhibition===
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The <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> of a serpin acts as a substrate for its cognate protease.
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The <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> of SCCA1 acts as a substrate for its target protease.
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The <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> is cleaved at a scissile bond between two residues <scene name='60/604473/P1_scene/3'>Ser354 termed P1 (N-terminal of the cleavage event) and Ser355 termed P1’ (C-terminal of the cleavage event)</scene>. The <scene name='60/604473/P1_scene/3'>P1 and P1' residues</scene> are critical for serpin specificity and mutation of these residues results in the loss or conversion of inhibitory activity. The protease recognize <scene name='60/604473/Amino_acids_for_protease_recog/1'>amino-acids of the RCL</scene> that allow its docking.
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The <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> is cleaved at a scissile bond between two residues <scene name='60/604473/P1_scene/3'>Ser354 termed P1 (N-terminal of the cleavage event) and Ser355 termed P1’ (C-terminal of the cleavage event)</scene>. The <scene name='60/604473/P1_scene/3'>P1 and P1' residues</scene> are the necessary condition for target protease specificity. Indeed, the mutation of these residues results destroys inhibitory activity. The protease recognize <scene name='60/604473/Amino_acids_for_protease_recog/1'>amino-acids of the RCL</scene> that allow its docking.
<ref>M. S. J. Mangan, D. Kaiserman & P. I. Bird, The role of serpins in vertebrate immunity
<ref>M. S. J. Mangan, D. Kaiserman & P. I. Bird, The role of serpins in vertebrate immunity
Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australiahttp://onlinelibrary.wiley.com/doi/10.1111/j.1399-0039.2008.01059.x/pdf DOI : 10.1111/j.1399-0039.2008.01059.x/pdf </ref> http://genome.cshlp.org/content/10/12/1845
Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australiahttp://onlinelibrary.wiley.com/doi/10.1111/j.1399-0039.2008.01059.x/pdf DOI : 10.1111/j.1399-0039.2008.01059.x/pdf </ref> http://genome.cshlp.org/content/10/12/1845
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[[Image:Fonction2.jpg|600px]] [[Image:fonction1.jpg|900px]]
[[Image:Fonction2.jpg|600px]] [[Image:fonction1.jpg|900px]]
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Prior to hydrolysis of the acyl-enzyme intermediate, the serpin rapidly undergoes the S-to-R transition. Since the <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> is still covalently attached to the protease via the ester bond, the S-to-R transition moves the protease from the top to the bottom of the serpin. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0104935 At the same time, the protease is distorted into a conformation, where the acyl enzyme intermediate is hydrolysed extremely slowly. The the active site of the enzyme would be expected to break.The protease thus remains covalently attached to the target protease and is thereby inhibited.
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Before the hydrolysis of the acyl-enzyme intermediate, the serpin rapidly undergoes from Stressed to Relaxed transition. The <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> remains covalently attached to the protease, however the protease is moved from the top to the bottom of SCCA1. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0104935
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This move induce a protease distortion into a conformation, in which the acyl enzyme intermediate is hydrolysed extremely slowly. The active site of the enzyme would be expected to break.The protease thus remains covalently attached to the target protease and is thereby inhibited.
[[Image:Gb-2006-7-5-216-1-l_-_Copie.jpg|600px]]
[[Image:Gb-2006-7-5-216-1-l_-_Copie.jpg|600px]]
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Further, since the serpin has to be cleaved to inhibit the target protases, inhibition consumes the serpin as well. Serpins are therefore irreversible enzyme inhibitors.
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Consequently, the serpin has to be cleaved to inhibit the target protases. Thus, SCCA1 is irreversible protease inhibitor.
<ref>J. A. HUNTINGTON,Department of Haematology, Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK, Serpin structure, function and dysfunction,
<ref>J. A. HUNTINGTON,Department of Haematology, Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK, Serpin structure, function and dysfunction,
http://onlinelibrary.wiley.com/doi/10.1111/j.1538-7836.2011.04360.x/pdf DOI : 10.1111/j.1538-7836.2011.04360.x/pdf</ref>
http://onlinelibrary.wiley.com/doi/10.1111/j.1538-7836.2011.04360.x/pdf DOI : 10.1111/j.1538-7836.2011.04360.x/pdf</ref>
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===JNK1 interaction===
===JNK1 interaction===
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SCCA1 also acts as an inhibitor of UV-induced apoptosis via suppression of the activity of c-Jun NH(2)-terminal kinase (JNK1). It is known that JNK1 is responsible for UV-induced apoptotic cell death and SCCA-1 is up-regulated in UV-irradiated and sun-exposed cells. SCCA1 binds to phosphorylated JNK1 and is transferred into the nucleus after UV irradiation.
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SCCA1 acts as an inhibitor of UV-induced apoptosis by suppressing the activity of JNK1 (c-Jun NH2-terminal kinase). It is known that JNK1 is responsible for UV-induced apoptotic cell death and SCCA-1 is up-regulated in UV-irradiated and sun-exposed cells. SCCA1 binds to phosphorylated JNK1 and is transferred into the nucleus after UV irradiation.
<ref>Chika Katagiri, Jotaro Nakanishi, Kuniko Kadoya, and Toshihiko Hibino, Serpin squamous cell carcinoma antigen inhibits
<ref>Chika Katagiri, Jotaro Nakanishi, Kuniko Kadoya, and Toshihiko Hibino, Serpin squamous cell carcinoma antigen inhibits
UV-induced apoptosis via suppression of c-JUN
UV-induced apoptosis via suppression of c-JUN
NH2-terminal kinase
NH2-terminal kinase
http://jcb.rupress.org/content/172/7/983.full.pdf+html DOI : 172/7/983.full.pdf+html </ref>
http://jcb.rupress.org/content/172/7/983.full.pdf+html DOI : 172/7/983.full.pdf+html </ref>
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Indeed the reactive center loop (<scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene>) of SCCA1 is very flexible and located away from the center of SCCA1. The inhibitory effect of SCCA1 on the kinase activity of JNK1 is lost when the <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> was truncated. Furthermore, a mutant protein created by replacing <scene name='60/604473/Phe_352/1'>one amino-acid</scene> in <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> maintain the suppressive activity to JNK1, whereas the inhibitory effect to proteinase is obviously decreased.
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Indeed the (<scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene>) of SCCA1 is an external and flexible domain of SCCA1. When the <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> is truncated, the inhibitory effect of SCCA1 on the kinase activity of JNK1 is lost.
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Moreover, a mutant protein created by replacing <scene name='60/604473/Phe_352/1'>one amino-acid</scene> in <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> even retains the suppressive activity against JNK1 but the inhibitory proteinase activity is reduced.
<ref> PMID : 19166818<ref>
<ref> PMID : 19166818<ref>
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This indicate that the exposed <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> of the native and mutated forms is essential for the JNK1 inhibitory activity, and the JNK1-interaction site is different from the site of proteinase. Actualy JNK1 may bind the the <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> region, except for the proteinase-binding site, or the center of <scene name='60/604473/A_beta_sheet/3'>A β-sheet</scene>. http://www.sciencedirect.com/science/article/pii/S0006291X09000953
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This indicate that the exposed <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> is essential for the JNK1 inhibitory activity, and that JNK1 interaction site is different from the proteinase site. Actualy JNK1 may bind the <scene name='60/604473/The_rcl_loop_scene/3'>RCL</scene> region, except the proteinase-binding site, or the center of <scene name='60/604473/A_beta_sheet/3'>A β-sheet</scene>. http://www.sciencedirect.com/science/article/pii/S0006291X09000953
===Receptor (LPR) interaction===
===Receptor (LPR) interaction===

Revision as of 13:14, 8 January 2015

SQUAMOUS CELL CARICNOMA ANTIGEN 1

Squamous cell carcinoma antigen 1 (PDB code 2zv6)

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