CBM20

CBM20, or carbohydrate-binding module family 20, is a family of small non-catalytic modules classified in the CAZy database. Members of CBM20 preferentially bind to starch and related glucans and are commonly found appended to starch-degrading enzymes such as alpha-amylases, starch-branching enzymes, and other hydrolases. The module enhances the efficiency of hydrolysis by increasing the local concentration of substrate at the catalytic site, particularly on insoluble or granular starch substrates.

Structure and binding properties: Most CBM20 members are compact single-domain modules of roughly 90–110 amino acids that adopt a beta-sandwich fold. Binding to starch is mediated by aromatic residues, especially tryptophan and tyrosine, which form stacking interactions with glucose rings. The affinity and specificity can vary among family members; some modules preferentially bind to amylose, others to amylopectin, and some exhibit broad affinity for granular starch.

Distribution and function: CBM20 modules are found across bacteria and fungi, frequently as components of multi-domain amylolytic enzymes. They serve to target and anchor enzymes to their starch substrates, thereby enhancing catalytic efficiency on particulate starch and aiding processes such as starch degradation in nature and industrial applications.

Related context: Carbohydrate-binding modules (CBMs) are non-catalytic domains that assist catalytic domains by improving substrate binding. CBM20 is one of several CBM families specialized for starch recognition and binding.