Structure-Reactivity Studies of Trichoderma reesei Cellobiohydrolase Cel7A

摘要

The major cellulase secreted by the filamentous fungus Trichoderma reesei is cellobiohydrolase Cel7A. It hydrolyzes the β-1,4-linkage of a cellulose chain by means of a double-displacement mechanism. A series of substituted aryl β-lactosides was used for reactivity studies. The Hammett plot shows that the formation of the glycosyl-enzyme intermediate is the rate-limiting step, also with highly activated substrates. A catalytic triad of carboxylate residues Glu212-Asp214-Glu217 is directly involved in the retaining mechanism. As previously revealed by protein X-ray crystallography, their specific function is presently confirmed by a detailed kinetic analysis of the mutants E212Q, D214N and E217Q.