InterPro: IPR001524 Glycoside hydrolase, family 6, conserved site

O-Glycosyl hydrolases EC:3.2.1. are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycosyl hydrolases, based on sequence similarity, has led to the definition of 85 different families [1, 2, 3]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) web site [4]. Because the fold of proteins is better conserved than their sequences, some of the families can be grouped in clans.

Glycoside hydrolase family 6 GH6 comprises enzymes with several known activities; endoglucanase (EC:3.2.1.4); cellobiohydrolase (EC:3.2.1.91). These enzymes were formerly known as cellulase family B.

The 3D structure of the enzymatic core of cellobiohydrolase II (CBHII) from the fungus Trichoderma reesei reveals an alpha-beta protein with a fold similar to the ubiquitous barrel topology first seen in triose phosphate isomerase [5]. The active site of CBHII is located at the C-terminal end of a parallel beta barrel, in an enclosed tunnel through which the cellulose threads. Two aspartic acid residues, located in the centre of the tunnel are the probable catalytic residues [5].