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)

Three insect peptides showing high sequence similarity and belonging to the same structural family incorporating a cysteine knot and a short three-stranded antiparalled beta-sheet were studied. Their inhibitory effect on two serine proteases (bovine alpha-chymotrypsin and human leukocyte elastase) is reported. One of them, PMP-C, is a strong alpha-chymotrypsin inhibitor (Ki = 0.2 nM) and interacts with leukocyte elastase with a Ki of 0.12 microM. The other two peptides, PMP-D2 and HI, interact only weakly with alpha-chymotrypsin and do not inhibit leukocyte elastase. Synthetic variants of these peptides were prepared by solid-phase synthesis, and their action toward serine proteases was evaluated. This enabled us to locate the P1 residues within the reactive sites (Leu-30 for PMP-C and Arg-29 for PMP-D2 and HI), and, interestingly, variants of PMP-D2 and HI were converted into powerful inhibitors of both alpha-chymotrypsin and leukocyte elastase, the most potent elastase inhibitor obtained in this study having a Ki of 3 nM.
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PMID:Serine protease inhibition by insect peptides containing a cysteine knot and a triple-stranded beta-sheet. 759 20

The solution structure and the disulfide pairings of a 36-residue proteinase inhibitor isolated from the insect Locusta migratoria have been determined using NMR spectroscopy and simulated annealing calculations. The peptide, termed PMP-C, was previously shown to inhibit bovine alpha-chymotrypsin as well as human leukocyte elastase, and was also found to block high-voltage-activated Ca2+ currents in rat sensory neurones. PMP-C has a prolate ellipsoid shape and adopts a tertiary fold hitherto unobserved in the large group of small "canonical" proteinase inhibitors. The over-all fold consists mainly of three strands arranged in a right-handed twisted, antiparallel, beta-sheet that demarcates a cavity, together with a linear amino-terminal segment oriented almost perpendicular to the three strands of the beta-sheet. Inside the cavity a phenyl ring constitutes the centre of a hydrophobic core. The proteinase binding loop is located in the carboxy-terminal part of the molecule, between two cysteine residues involved in disulfide bridges. Its conformation resembles that found in other small canonical proteinase inhibitors. A comparison of PMP-C structure with the recently published solution structure of the related peptide PMP-D2 shows that the most significant differences are complementary changes involved in the stabilization of similar folds. This comparison led us to review the structure of PMP-D2 and to identify two salt bridges in PMP-D2.
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PMID:Solution structure of PMP-C: a new fold in the group of small serine proteinase inhibitors. 861 85

The crystal structures of two homologous inhibitors (PMP-C and PMP-D2v) from the insect Locusta migratoria have been determined in complex with bovine alpha-chymotrypsin at 2.1- and 3.0-A resolution, respectively. PMP-C is a potent bovine alpha-chymotrypsin inhibitor whereas native PMP-D2 is a weak inhibitor of bovine trypsin. One unique mutation at the P1 position converts PMP-D2 into a potent bovine alpha-chymotrypsin inhibitor. The two peptides have a similar overall conformation, which consists of a triple-stranded antiparallel beta-sheet connected by three disulfide bridges, thus defining a novel family of serine protease inhibitors. They have in common the protease interaction site, which is composed of the classical protease binding loop (position P5 to P'4, corresponding to residues 26-34) and of an internal segment (residues 15-18), held together by two disulfide bridges. Structural divergences between the two inhibitors result in an additional interaction site between PMP-D2v (position P10 to P6, residues 21-25) and the residues 172-175 of alpha-chymotrypsin. This unusual interaction may be responsible for species selectivity. A careful comparison of data on bound and free inhibitors (from this study and previous NMR studies, respectively) suggests that complexation to the protease stabilizes the flexible binding loop (from P5 to P'4).
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PMID:Complexation of two proteic insect inhibitors to the active site of chymotrypsin suggests decoupled roles for binding and selectivity. 1149 15

PMP-D2 and HI, two peptides from Locusta migratoria, were shown to belong to the family of tight-binding protease inhibitors. However, they interact weakly with bovine trypsin (K(i) around 100 nM) despite a trypsin-specific Arg at the primary specificity site P1. Here we demonstrate that they are potent inhibitors of midgut trypsins isolated from the same insect and of a fungal trypsin from Fusarium oxysporum (K(i) <or= 0.02 nM). Therefore, they display a selectivity not existing for the parent chymotrypsin inhibitor PMP-C. By NMR, we demonstrate that HI possesses a highly rigid structure similar to the crystal structure of a variant of PMP-D2 in complex with bovine alpha-chymotrypsin. The main difference with PMP-C is located in the region from residues 20 to 24 (positions P6-P10) that interacts with the loop containing Gly173 in chymotrypsin. The corresponding residue in mammalian trypsins is always a proline that may generate a steric clash with the inhibitor. The residues thought to confer selectivity were mutated with PMP-C as a model. The resulting analogue PMP-D2(K10W,P21A,W25A) loses some activity toward insect and fungal trypsins but is a more potent inhibitor of mammalian trypsins, corresponding to a decrease of selectivity. This work represents a first attempt in tuning the selectivity of natural peptidic serine protease inhibitors by mutating residues out of the reactive loop (P3-P'3).
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PMID:Selective inhibition of trypsins by insect peptides: role of P6-P10 loop. 1462 7