Proteinase: Difference between revisions
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<StructureSection load='' size='350' side='right' scene='Journal:JBSD:39/Cv/11' caption=''> | <StructureSection load='' size='350' side='right' scene='Journal:JBSD:39/Cv/11' caption=''> | ||
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==Function== | |||
'''Proteinase''' (PRO) are enzymes which hydrolyze peptide bonds. They are classified by the amino acid site of their cleavage or by the pH at which they are active.<br /> | '''Proteinase''' (PRO) are enzymes which hydrolyze peptide bonds. They are classified by the amino acid site of their cleavage or by the pH at which they are active.<br /> | ||
* '''PRO B''' is a serine protease<ref>PMID:3325823</ref>. For more details see [[Streptomyces griseus proteinase B]].<br /> | * '''PRO B''' is a serine protease<ref>PMID:3325823</ref>. For more details see [[Streptomyces griseus proteinase B]].<br /> | ||
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For '''cysteine PRO''' from ''Trypanosoma cruzi'' see [[Cruzain]]. | For '''cysteine PRO''' from ''Trypanosoma cruzi'' see [[Cruzain]]. | ||
== The remarkable efficiency of a Pin-II proteinase inhibitor sans two conserved disulfide bonds is due to enhanced flexibility and hydrogen-bond density in the reactive loop <ref>doi 10.1080/07391102.2012.745378</ref> == | |||
Background: Plant proteinase Inhibitors (PIs) are ubiquitous in the plant kingdom and have been extensively studied as plant defense molecules, which inhibit hydrolytic enzymes (''e.g.'' <scene name='Journal:JBSD:39/Cv/12'>trypsin</scene>, <font color='darkmagenta'><b>colored in darkmagenta</b></font>) of the insect gut <ref name="Green">PMID: 17836138</ref>. Among various PI families, Serine PI Pin-II/Pot-II family displays a remarkable structural and functional diversity at the gene and protein level <ref name="Kong">PMID: 18315854</ref>. Wound, herbivory and stress induced up-regulation of these PIs clearly link them to plant defense <ref name="Green">PMID: 17836138</ref>. Previous studies using transgenic systems or in vivo assays have positively correlated the advantage offered by Pin-II PI expression in plants against insect attack <ref name="Johnson">PMID: 2602379</ref> <ref name="Duan">PMID: 9630927</ref>. Precursor proteins of Pin-II PIs consist of 1- to 8- <scene name='Journal:JBSD:39/Cv/4'>inhibitory repeat domains (IRDs)</scene> connected by proteolytic-sensitive linkers, which releases IRD units upon cleavage. <scene name='Journal:JBSD:39/Cv/5'>Each IRD is a peptide of around 50 aa length</scene> (<span style="color:lime;background-color:black;font-weight:bold;">colored in green</span>) with a molecular mass of ~6 KDa. The aa sequence of IRDs shows variations, at the same time the <scene name='Journal:JBSD:39/Cv/6'>8 cysteine residues that form disulfide bridge are conserved</scene> (<span style="color:yellow;background-color:black;font-weight:bold;">colored in yellow</span>) <ref name="Nielsen">PMID: 7578034</ref> <ref name="Scanlon">PMID: 10425681</ref> <ref name="Lee">PMID: 10360353</ref> <ref name="Schirra">PMID: 11178894</ref>. One structural feature of Pin-II IRD is a disordered loop with triple stranded β sheet scaffold. The disordered solvent exposed reactive loop is anchored by the four conserved disulfide bonds (C4-C41, C7-C25, C8-C37 and C14-C50) <ref name="Schirra1">PMID: 16029154</ref> <ref name="Schirra2">PMID: 18991765</ref>. Among the four disulfide bonds, C8-C37 has been found to be very crucial for maintaining active conformation, whereas C4-C41 has an important role in maintaining the flexibility of the reactive loop <ref name="Schirra3">PMID: 19925809</ref>. Thus, any selective loss of disulfide bond is expected to have evolutionary significance leading to functional differentiation of inhibitors <ref name="Li">PMID: 21494600</ref>. | Background: Plant proteinase Inhibitors (PIs) are ubiquitous in the plant kingdom and have been extensively studied as plant defense molecules, which inhibit hydrolytic enzymes (''e.g.'' <scene name='Journal:JBSD:39/Cv/12'>trypsin</scene>, <font color='darkmagenta'><b>colored in darkmagenta</b></font>) of the insect gut <ref name="Green">PMID: 17836138</ref>. Among various PI families, Serine PI Pin-II/Pot-II family displays a remarkable structural and functional diversity at the gene and protein level <ref name="Kong">PMID: 18315854</ref>. Wound, herbivory and stress induced up-regulation of these PIs clearly link them to plant defense <ref name="Green">PMID: 17836138</ref>. Previous studies using transgenic systems or in vivo assays have positively correlated the advantage offered by Pin-II PI expression in plants against insect attack <ref name="Johnson">PMID: 2602379</ref> <ref name="Duan">PMID: 9630927</ref>. Precursor proteins of Pin-II PIs consist of 1- to 8- <scene name='Journal:JBSD:39/Cv/4'>inhibitory repeat domains (IRDs)</scene> connected by proteolytic-sensitive linkers, which releases IRD units upon cleavage. <scene name='Journal:JBSD:39/Cv/5'>Each IRD is a peptide of around 50 aa length</scene> (<span style="color:lime;background-color:black;font-weight:bold;">colored in green</span>) with a molecular mass of ~6 KDa. The aa sequence of IRDs shows variations, at the same time the <scene name='Journal:JBSD:39/Cv/6'>8 cysteine residues that form disulfide bridge are conserved</scene> (<span style="color:yellow;background-color:black;font-weight:bold;">colored in yellow</span>) <ref name="Nielsen">PMID: 7578034</ref> <ref name="Scanlon">PMID: 10425681</ref> <ref name="Lee">PMID: 10360353</ref> <ref name="Schirra">PMID: 11178894</ref>. One structural feature of Pin-II IRD is a disordered loop with triple stranded β sheet scaffold. The disordered solvent exposed reactive loop is anchored by the four conserved disulfide bonds (C4-C41, C7-C25, C8-C37 and C14-C50) <ref name="Schirra1">PMID: 16029154</ref> <ref name="Schirra2">PMID: 18991765</ref>. Among the four disulfide bonds, C8-C37 has been found to be very crucial for maintaining active conformation, whereas C4-C41 has an important role in maintaining the flexibility of the reactive loop <ref name="Schirra3">PMID: 19925809</ref>. Thus, any selective loss of disulfide bond is expected to have evolutionary significance leading to functional differentiation of inhibitors <ref name="Li">PMID: 21494600</ref>. | ||