Extremophilic Carbohydrate Active Enzymes (CAZymes)

Carbohydrate active enzymes (CAZymes) are a large class of enzymes, which build and breakdown the complex carbohydrates of the cell. On the basis of their amino acid sequences they are classified in families that show conserved catalytic mechanism, structure, and active site residues, but may conflict each other in substrate specificity. The CAZymes provides a continuously updated list of the glycoside hydrolase families, GHs. This group of enzymes is classified based on functional similarity, but today they are classified into 108 GHs on the basis of amino acid sequence similarity. Despite their similarities to enzymes with known functions, their primary functions are still unclear. Based on these criteria, β-galactosidase activities are now divided into four different families: GH1, GH2, GH35 and GH42, among which the better studied GH2 includes β-galactosidase from Escherichia coli, Aspergillus, Bacillus megatherium, and Sulfolobus solfataricus, while those from thermophilic, psychrophilic and halophilic organisms belong to GH42. Lactase is often confused as an alternate name for β-galactosidase, but it is actually simply a subclass (small subunit) of β-galactosidase.