InterPro: IPR000556 Glycoside hydrolase, 48F

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 48 GH48 comprises enzymes with several known activities; endoglucanase (EC:3.2.1.4); cellobiohydrolase (EC:3.2.1.91).

The largest cellulase gene sequenced to date is one of the cellulases (celA) from the genome of the thermophilic anaerobic bacterium Caldocellum saccharolyticum. The celA gene product is a polypeptide of 1751 amino acids; this has a multidomain structure comprising two catalytic domains and two cellulose-binding domains, linked by Pro-Thr-rich regions. The N-terminal domain encodes an endoglucanase activity on carboxymethylcellulose, consistent with its similarity to several endo-1, 4-beta-D-glucanase sequences. The C-terminal domain shows similarity to a cellulase from Clostridium thermocellum (CelS), which acts synergistically with a second component to hydrolyse crystalline cellulose [5].