InterPro: IPR000334 Glycoside hydrolase, family 45

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 45 GH45 comprises enzymes with only one known activity; endoglucanase (EC:3.2.1.4).

The microbial degradation of cellulose and xylans requires several types of enzymes such as endoglucanases, cellobiohydrolases (EC:3.2.1.91) (exoglucanases), or xylanases (EC:3.2.1.8) [5, 6]. Fungi and bacteria produce a spectrum of cellulolytic enzymes (cellulases) and xylanases which, on the basis of sequence similarities, can be classified into families. One of these families is known as the cellulase family K or as the glycosyl hydrolases family 45 [7]. The best conserved regions in these enzymes is located in the N-terminal section. It contains an aspartic acid residue which has been shown [8] to act as a nucleophile in the catalytic mechanism. This also has several cysteines that are involved in forming disulphide bridges.