Many glycoside hydrolases are modular proteins composed of catalytic modules appended to one or more non-catalytic carbohydrate-binding modules (CBMs). CBMs bind to a range of polysaccharides that include crystalline cellulose and hemicelluloses such as glucan, xylan, mannan, and glucomannan. The main function of CBMs is to increase the catalytic efficiency of the enzymes against soluble and/or insoluble substrates by bringing the catalytic module into prolonged and intimate contact with its substrate. So far many CBMs have been identified and are classified into 43 different families in the CAZy database based on sequence similarity and biochemical function.

This entry represents the family 31 carbohydrate-binding module (CBM31) of beta-1,3-xylanase PMID:16061225. Beta-1,3-xylan is a homopolymer of b-1,3-linked D-xylose and is a polysaccharide peculiar to marine algae and it is hydrolized by Beta-1,3-xylanase PMID:10742274.