3tgk

From Proteopedia

Revision as of 18:32, 18 December 2007

TRYPSINOGEN MUTANT D194N AND DELETION OF ILE 16-VAL 17 COMPLEXED WITH BOVINE PANCREATIC TRYPSIN INHIBITOR (BPTI)

Overview

The contribution of induced fit to enzyme specificity has been much, debated, although with little experimental data. Here we probe the effect, of induced fit on enzyme specificity using the trypsin(ogen) system. BPTI, is known to induce trypsinogen to assume a trypsinlike conformation., Correlations are observed between BPTI affinity and the values of, k(cat)/K(m) for the hydrolysis of two substrates by eight trypsin(ogen), variants. The slope of both correlations is -1.8. The crystal structures, of the BPTI complexes of four variant trypsinogens were also solved. Three, of these enzymes, K15A, DeltaI16V17/D194N, and DeltaI16V17/Q156K, trypsinogen, are 10- to 100-fold more active than trypsinogen. The fourth, variant, DeltaI16V17 trypsinogen, is the lone outlier in the correlations;, its activity is lower than expected based on its affinity for BPTI. The S1, site and oxyanion hole, formed by segments 184A-194 and 216-223, are, trypsinlike in all of the enzymes. These structural and kinetic data, confirm that BPTI induces an active conformation in the trypsin(ogen), variants. Thus, changes in BPTI affinity monitor changes in the energetic, cost of inducing a trypsinlike conformation. Although the S1 site and, oxyanion hole are similar in all four variants, the N-terminal and, autolysis loop (residues 142-152) segments have different interactions for, each variant. These results indicate that zymogen activity is controlled, by a simple conformational equilibrium between active and inactive, conformations, and that the autolysis loop and N-terminal segments control, this equilibrium. Together, these data illustrate that induced fit does, not generally contribute to enzyme specificity.

About this Structure

3TGK is a Protein complex structure of sequences from Bos taurus and Rattus norvegicus with CA and SO4 as ligands. Active as Trypsin, with EC number 3.4.21.4 Known structural/functional Site: . Full crystallographic information is available from OCA.

Reference

The energetic cost of induced fit catalysis: Crystal structures of trypsinogen mutants with enhanced activity and inhibitor affinity., Pasternak A, White A, Jeffery CJ, Medina N, Cahoon M, Ringe D, Hedstrom L, Protein Sci. 2001 Jul;10(7):1331-42. PMID:11420435

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