Cellobiohydrolases: Role, Mechanism, and Recent Developments

Abstract

Cellobiohydrolases or exoglucanases are produced by various bacteria and fungi with catalytic modules belonging to families 5, 6, 7, 9, 48, and 74 glycoside hydrolases, which act at the chains end of cellulose resulting in release of glucose as well as cellobiose. The CBH I and II works processively from reducing and nonreducing ends of the cellulose chain, respectively. The catalytic module of CBHs is the tunnel structure formed by two surface loops that may covers entirety or part of active site evidenced that the mode of action proceeds in a processive manner as cellobiohydrolase progresses along the cellulose chain. CBHs are able to work actively in the crystalline region of cellulose, probably peeling them from the microcrystalline structure of Avicel. Although several assays have been proposed, no specific substrate as well as assay method to measure exoglucanases has been described till date. In recent days, several new approaches such as δ-sequence mediated integration, SCHEMA, and FoldX and a 'consensus' sequence have been developed to improve activity and stability of CBHs.