1cb2

From Proteopedia

Revision as of 13:53, 5 November 2007

CELLOBIOHYDROLASE II, CATALYTIC DOMAIN, MUTANT Y169F

Overview

Trichoderma reesei cellobiohydrolase II (CBHII) is an exoglucanase, cleaving primarily cellobiose units from the non-reducing end of cellulose, chains. The beta-1,4 glycosidic bond is cleaved by acid catalysis with an, aspartic acid, D221, as the likely proton donor, and another aspartate, D175, probably ensuring its protonation and stabilizing charged reaction, intermediates. The catalytic base has not yet been identified, experimentally. The refined crystal structure of CBHII also shows a, tyrosine residue, Y169, located close enough to the scissile bond to be, involved in catalysis. The role of this residue has been studied by, introducing a mutation Y169F, and analysing the kinetic and binding, behavior of the mutated CBHII. The crystal structure of the mutated enzyme, was determined to 2.0 A resolution showing no changes when compared with, the structure of native CBHII. However, the association constants of the, mutant enzyme for cellobiose and cellotriose are increased threefold and, for 4-methylumbelliferyl cellobioside over 50-fold. The catalytic, constants towards cellotriose and cellotetraose are four times lower for, the mutant. These data suggest that Y169, on interacting with a glucose, ring entering the second subsite in a narrow tunnel, helps to distort the, glucose ring into a more reactive conformation. In addition, a change in, the pH activity profile was observed. This indicates that Y169 may have a, second role in the catalysis, namely to affect the protonation state of, the active site carboxylates, D175 and D221.

About this Structure

1CB2 is a Single protein structure of sequence from Hypocrea jecorina with NAG and MAN as ligands. Active as Cellulose 1,4-beta-cellobiosidase, with EC number 3.2.1.91 Structure known Active Sites: ST1 and ST2. Full crystallographic information is available from OCA.

Reference

The active site of Trichoderma reesei cellobiohydrolase II: the role of tyrosine 169., Koivula A, Reinikainen T, Ruohonen L, Valkeajarvi A, Claeyssens M, Teleman O, Kleywegt GJ, Szardenings M, Rouvinen J, Jones TA, Teeri TT, Protein Eng. 1996 Aug;9(8):691-9. PMID:8875646

Page seeded by OCA on Mon Nov 5 15:58:29 2007