Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.1 (chymotrypsin)
10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Modeling studies have ascribed the remarkable resistance of thrombin to inhibition by the Kunitz type inhibitors, bovine pancreatic trypsin inhibitor (BPTI), and tissue factor pathway inhibitor (TFPI), to steric inhibition by the 60-loop insertion, especially Trp60D (in the chymotrypsin numbering system). Indeed, deletion of Pro60B, Pro60C, and Trp60D from this loop (des-PPW) enhances BPTI inhibition (Ki = 16 nM) (Le Bonniec, B. F., Guinto, E. R., MacGillivray, R. T. A., Stone, S. R., and Esmon, C. T. (1993) J. Biol. Chem. 268, 19055-19061). Activated protein C, however, lacks an equivalent insertion loop but is nevertheless resistant to inhibition by these Kunitz inhibitors. A unique feature of thrombin and activated protein C is the presence of Glu at position 192. Substitution of Glu192 with Gln in activated protein C dramatically enhances inhibition by BPTI and TFPI (Rezaie, A. and Esmon, C. T. (1993) J. Biol. Chem. 268, 19943-19948). We now demonstrate that thrombin E192Q (the Glu192-->Gln mutant) is inhibited by BPTI (Ki = 24 nM) or TFPI (Ki = 14 nM) much more effectively than wild type thrombin (Ki > 1 microM for both inhibitors). A thrombin mutant having both the des-PPW deletion and E192Q substitution binds BPTI (Ki = 35 pM) and TFPI (Ki = 25 pM) even tighter. BPTI can displace dansylarginine N-(-3-ethyl-1,5-pentanediyl)-amide from the active site of thrombin E192Q (Ki = 19 nM), indicating that BPTI interacts directly with the S1 binding site in thrombin. The E192Q mutation and PPW deletion contribute comparably and additively to the binding energy of thrombin with the Kunitz inhibitors. We suggest that access to the active center of thrombin is less restricted than predicted from previous studies.
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PMID:Glu192-->Gln substitution in thrombin yields an enzyme that is effectively inhibited by bovine pancreatic trypsin inhibitor and tissue factor pathway inhibitor. 751 31

The human intracellular serine proteinase inhibitor, proteinase inhibitor 6 (PI-6), was expressed in the methylotropic yeast Pichia pastoris. The PI-6 cDNA was modified to encode six histidine residues immediately after the initiation codon, and was placed under the control of the P. pastoris alcohol oxidase promoter in the vector pHIL-D2. On the methanol induction, active recombinant PI-6 was produced within the yeast cells, and following cell lysis, was separated from yeast proteins by affinity chromatography using nickel nitrilo-tri-acetic acid (NTA) resin. The interaction of recombinant PI-6 with a range of serine proteinases was studied. Second order association rate constants (ka) were derived for the interaction with trypsin (1.8 x 10(6) M-1 s-1), thrombin (1.2 x 10(5) M-1 s-1), urokinase plasminogen activator (4.0 x 10(4) M-1 s-1), plasmin (1.3 x 10(6) M-1 s-1), and activated protein C (7.5 x 10(3) M-1 s-1). By monitoring complex formation, recombinant PI-6 was also shown to interact with factor Xa. No complex formation was observed with chymotrypsin, human leukocyte elastase, cathepsin G and tissue plasminogen activator, although PI-6 is apparently a substrate for chymotrypsin, leukocyte elastase and cathepsin G.
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PMID:Production and characterization of recombinant human proteinase inhibitor 6 expressed in Pichia pastoris. 754 63

Mutation of residue 192 (chymotrypsin numbering) from Glu to Gln in thrombin and activated protein C has been shown to dramatically alter substrate and inhibitor specificity, in large part by allowing these enzymes to accept substrates with acidic residues in the P3 and/or P3' positions. In factor Xa, residue 192 is already a Gln. We now compare the properties of a Q192E mutant of Gla-domainless factor X (GDFX). Kinetic analysis of prothrombin activation indicates similar affinity of factor Va for GDFXa and GDFXa Q192E (Kd(app) = 3.6 and 3.7 microM, respectively). Prothrombin activation rates are similar for both enzymes with factor Va, but are approximately 10-fold slower for the Q192E mutant without factor Va. This defect is in the activation of prethrombin 2 and is corrected by factor Va only in the presence of fragment 2. Without factor Va, fragment 2 has no influence on bovine prethrombin 2 activation by GDFXa, but fragment 2 enhances prethrombin 2 activation by the Q192E mutant at least 10-fold. These results indicate that the fragment 2 domain of prothrombin probably alters the conformation of the prethrombin 2 domain, selectively improving its presentation to GDFXa Q192E. With respect to inhibition, tissue factor pathway inhibitor and bovine pancreatic trypsin inhibitor are > or = 30 times poorer inhibitors of GDFXa Q192E than of GDFXa, but these enzymes are inhibited at comparable rates by antithrombin. These results indicate that Gln-192 in factor Xa is a key determinant of substrate/inhibitor specificity.
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PMID:Contribution of residue 192 in factor Xa to enzyme specificity and function. 760 83

Z-D-Phe-Pro-boroMpg-OPin (9a)1,2 has been shown previously to be a highly specific inhibitor of thrombin in spite of lacking an arginine-like guanidino group at the P1 site. A range of compounds have been synthesized based upon this lead compound, varying the neutral side chain at the P1 site. Of the 20 examples based upon the structures at P2 and P3 of Z-D-X-Pro (X being Phe or beta,beta-diphenylalanine), all were found to be effective inhibitors of thrombin (Ki's between 10 and 100 nM). Furthermore all exhibited a high specificity toward thrombin having values for a Ki(trypsin)/Ki(thrombin) ratio of between 10- and 100-fold. High ratio values were found for a number of the compounds tested against a range of serine proteinases (plasmin, factor Xa, kallikrein, urokinase, protein Ca, chymotrypsin, elastase, and cathepsin G). As far as potency toward thrombin, compounds containing the methoxypropyl group at P1 were favored over those with a methoxy grouping on a shorter alkyl chain (8) or without the methoxy group (1-5). The compounds display potent anticoagulant activity with values for 18 in thrombin time of 0.63 microM and in activated partial thromboplastin time of 2.0 microM. 11B NMR has been used to confirm interaction of the boron atom with the active site. From the high specificity shown with all the compounds we propose that the compounds, constitute a new class of thrombin inhibitors.
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PMID:Characterization of a class of peptide boronates with neutral P1 side chains as highly selective inhibitors of thrombin. 773 10

Binding Ca2+ to a high affinity site in protein C and Gla-domainless protein C (protein C lacking residues 1-44) results in a conformational change that is required for activation by the thrombin-thrombomodulin complex, the natural activator of protein C. Protein C modeling studies suggested the single high affinity Ca2+ binding-site might be present in a loop in the protease domain and involve Glu-70 and -80 (chymotrypsin numbering system). This loop, which is a known Ca(2+)-binding site in trypsin, is also conserved in other coagulation proteases, including factors VII, IX,and X. In thrombin, which does not bind Ca2+, Glu-70 is replaced by Lys, creating an internal salt bridge with Glu-80. We constructed and expressed a Gla-domainless protein C mutant in which Glu-80 is replaced with Lys. The activation of the resultant mutant is accelerated by thrombomodulin in a Ca(2+)-independent fashion. Unlike wild type Gla-domainless protein C, Ca2+ no longer inhibits activation of the mutant by free thrombin, and Ca2+ stimulation of chromogenic activity is also absent. The characteristic Ca(2+)-dependent quenching of Gla-domainless protein C intrinsic fluorescence is also absent in the mutant. We conclude that the high affinity Ca(2+)-binding site in protein C critical for zymogen activation involves Glu-80. The Glu-80 to Lys mutation probably results in a salt bridge with Glu-70 that stabilizes protein C zymogen in a conformation similar, if not identical, to the Ca(2+)-stabilized conformation favorable for rapid activation by the thrombin-thrombomodulin complex.
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PMID:Mutation of Glu-80-->Lys results in a protein C mutant that no longer requires Ca2+ for rapid activation by the thrombin-thrombomodulin complex. 790 67

Protein C is a vitamin K-dependent serine protease zymogen that upon activation inhibits the coagulation cascade by inactivating factors Va and VIIIa. In an attempt to improve the anticoagulant activity of activated protein C (APC), we have prepared a mutant of protein C in mammalian cells in which Glu at position 192 (chymotrypsin numbering system) has been replaced with Gln (PC E192Q). Our strategy is based on the observation that the same substitution in thrombin improves the catalytic activity toward natural and synthetic substrates that contain Asp residues at P3 and P3'. Since factor Va also has an Asp at position P3 in the APC cleavage site of the factor Va heavy chain, we hypothesized that APC E192Q would inactivate factor Va more rapidly than wild type APC. The mutant inactivated factor Va approximately 2-3-fold faster than wild type. In plasma the mutant exhibited slightly less anticoagulant activity than wild type enzyme. Further characterization revealed that APC E192Q is inhibited 280 times faster than APC by alpha 1-antitrypsin (K2 = 2.8 x 10(3) M-1S-1 versus 10 M-1 S-1), and unlike APC, APC E192Q is inhibited by antithrombin III in the presence of heparin (K2 = 1.17 x 10(3) M-1 S-1) M-1 S-1) and absence of heparin (K2 = 57 M-1 S-1). Ca2+ increased K2 more than 4-fold with or without heparin. Unlike wild type APC, APC E192Q was effectively inhibited by pancreatic trypsin inhibitor (Ki = 10.6 +/- 0.26 nM) and tissue factor pathway inhibitor (58 +/- 5 nM). Like factor Xa, APC E192Q rapidly processed factor IX to factor IX alpha. These observations suggest that even though Glu at position 192 is not an optimal residue for catalyzing factor Va inactivation, it is an evolutionary adaptation to slow inhibition by plasma protease inhibitors.
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PMID:Conversion of glutamic acid 192 to glutamine in activated protein C changes the substrate specificity and increases reactivity toward macromolecular inhibitors. 810 82

Ecotin, a serine protease inhibitor found in the periplasm of Escherichia coli, has been characterized as an extremely potent anticoagulant and reversible tight-binding inhibitor of human factor Xa (FXa). The ecotin gene was cloned by PCR, highly expressed in E. coli, and purified from the E. coli periplasm. The binding of ecotin to FXa was stoichiometric with an equilibrium dissociation constant Ki of 54 pM. The association rate constant was 1.35 x 10(6) M-1 s-1, and the dissociation rate constant, measured in the presence of human leukocyte elastase (HLE) to prevent reassociation of ecotin with FXa, was 6.5 x 10(-5) s-1. Ecotin prolonged clotting time ca. 10-fold at 0.3 microM and at 2 microM in activated partial thromboplastin time and prothrombin time assays, respectively. Ecotin did not effectively inhibit the human plasma proteases thrombin, tissue factor.factor VIIa, factor XIa, activated protein C, plasmin, or tissue plasminogen activator (t-PA); however, it did potently inhibit factor XIIa, plasma kallikrein, HLE, and bovine trypsin and chymotrypsin. Coincubation of ecotin and FXa at 10 microM each resulted in a (ecotin)2.(FXa)2 complex as determined by gel filtration. Dimerization of ecotin alone was measured by fluorescence titration which yielded a Kd of ca. 390 nM. FXa cleaved ecotin slowly at pH 4.0 between M84 and M85. Replacement of the P1 Met84 residue with Arg and Lys led to FXa inhibitors with Ki values of 11 and 21 pM, respectively. The P1 Arg and Lys mutants also significantly inhibited thrombin, factor XIa, activated protein C, plasmin, factor XIIa, kallikrein, and bovine trypsin and chymotrypsin but did not inhibit tissue factor.factor VIIa, t-PA, or HLE.
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PMID:Ecotin is a potent anticoagulant and reversible tight-binding inhibitor of factor Xa. 814 99

A patient with recurrent deep vein thrombosis and heterozygous type II deficiency, characterized by reduced protein C activity in both amidolytic and clotting functional assays, was investigated by direct sequencing of PCR fragments derived from the coding portion of the protein C gene. AG (8856) to A transition was noted in the patient which was not present in healthy controls. This mutation is predicted to cause the substitution of Ser for Gly 381, an evolutionari'y conserved residue in the substrate binding pocket of serine-proteases (Gly 216, chymotrypsin numbering). A computer model of the structure of the serine-protease domain indicates that the properties of the altered protein C molecule can be explained on the basis of steric hindrance between the substituted serine and the substrate arginine side chains.
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PMID:Symptomatic type II protein C deficiency caused by a missense mutation (Gly 381-->Ser) in the substrate-binding pocket. 839 32

Barley serpin BSZx is a potent inhibitor of trypsin and chymotrypsin at overlapping reactive sites (Dahl, S.W., Rasmussen, S.K. and Hejgaard, J. (1996) J. Biol. Chem., in press). We have now investigated the interactions of BSZx with a range of serine proteinases from human plasma, pancreas and leukocytes, a fungal trypsin and three subtilisins. Thrombin, plasma kallikrein, factor VIIa/tissue factor and factor Xa were inhibited by BSZx at heparin independent association rates (k(ass)) of 4.5 X 10(3)-1.3 x 10(5) M(-1) s(-1) at 22 degrees C. Only factor Xa turned a significant fraction of BSZx over as substrate. Complexes of these proteinase with BSZx resisted boiling in SDS, and amino acid sequencing showed that cleavage in the reactive center loop only occurred after P1 Arg. Activated protein C and leukocyte elastase were slowly inhibited by BSZx (k(ass)=1-2 x 10(2) M(-1) s(-1)) whereas factor XIIa, urokinase and tissue type plasminogen activator, plasmin and pancreas kallikrein and elastase were not or only weakly affected. The inhibition pattern with mammalian proteinases reveal a specificity of BSZx similar to that of antithrombin III. Trypsin from Fusarium was not inhibited while interaction with subtilisin Carlsberg and Novo was rapid but most BSZx was cleaved as a substrate. Identification of a monoclonal antibody specific for native BSZx indicate that complex formation and loop cleavage result in similar conformational changes.
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PMID:Inhibition of coagulation factors by recombinant barley serpin BSZx. 884 56

The kinetic parameters were determined for the hydrolysis of a peptide based on the activation site of the thrombin receptor (residues 38-60) by thrombin and 12 other proteases. The kcat and Km values for the cleavage of this peptide (TR39-40) by thrombin were 107 s-1 and 1.3 microM; the kcat/Km of TR39-40 is among the highest observed for thrombin. A model is presented that reconciles the parameters for cleavage of the peptide with the concentration dependence of cellular responses to thrombin. Cleavage of TR39-40 was not specific for thrombin. The pancreatic proteases trypsin and chymotrypsin hydrolysed TR39-40 efficiently (kcat/Km > 10(6) M-1.s-1). Whereas trypsin cleaved TR39-40 at the thrombin activation site (Arg41-Ser42), chymotrypsin hydrolysed the peptide after Phe43. This chymotryptic cleavage would result in inactivation of the receptor. The efficient cleavage of TR39-40 by chymotrypsin (kcat/Km approximately 10(6) M-1.s-1) was predominantly due to a low Km value (2.8 microM). The proteases factor Xa, plasmin, plasma kallikrein, activated protein C and granzyme A also hydrolysed TR39-40 at the Arg41-Ser43 bond, but exhibited kcat/Km values that were at least 10(3)-fold lower than that observed with thrombin. Both tissue and urokinase plasminogen activators as well as granzyme B and neutrophil elastase were unable to cleave TR39-60 at appreciable rates. However, neutrophil cathepsin G hydrolysed the receptor peptide after Phe55. Like the chymotryptic cleavage, this cleavage would lead to inactivation of the receptor, but the cathepsin G reaction was markedly less efficient; the kcat/K(m) value was almost four orders of magnitude lower than that for thrombin. In addition to the above cleavage sites, a secondary site for thrombin and other arginine-specific proteases was identified at Arg46, but the cleavage at this site only occurred at very low rates and is unlikely to be significant in vivo.
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PMID:Cleavage of the thrombin receptor: identification of potential activators and inactivators. 894 6


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