InterPro: IPR005084 Carbohydrate binding domain, family 6

Carbohydrate-binding modules (CBMs) of microbial glycoside hydrolases play a central role in the recycling of photosynthetically fixed carbon through their binding to specific plant structural polysaccharides [1]. Carbohydrate-binding modules (CBMs) can recogise both crystalline and amorphous cellulose forms [2]. CBMs are the most common non-catalytic modules associated with enzymes active in plant cell-wall hydrolysis. Many putative CBMs have been identified by amino acid sequence alignments but only a few representatives have been show experimentally to have a carbohydrate-binding function [3].

CBM11 binds both beta-1,4-glucan and beta-1,3-1,4-mixed linked glucans. CBM15 binds to xylan and xylooligosaccharides. CBM25 has a starch-binding function. CBM17 binds to amorphous cellulose and soluble beta-1,4-glucans, with a minimal binding requirement of cellotriose and optimal affinity for cellohexaose. Family 17 CBMs appear to have a very shallow binding cleft that may be more accessible to cellulose chains in non-crystalline cellulose than the deeper binding clefts of family 4 CBMs [4]. CBM28 does not compete with CBM17 modules when binding to non-crystalline cellulose but does have a "beta-jelly roll" topology, which is similar in structure to the CBM17 domains. Sequence and structural conservation in families 17 and 28 suggests that they have evolved through gene duplication and subsequent divergence [2].

The carbohydrate-binding module, family 6 CBM6 [5] was previously known as cellulose-binding domain family VI (CBD VI). The cellulose-binding function has been demonstrated in one case on amorphous cellulose and xylan. Some of these modules also bind beta-1,3-glucan.