Carbohydrate binding module family 20 (IPR002044)

Short name: CBM_fam20

Overlapping homologous superfamilies

Domain relationships


A carbohydrate-binding module (CBM) is defined as a contiguous amino acid sequence within a carbohydrate-active enzyme with a discreet fold having carbohydrate-binding activity. A few exceptions are CBMs in cellulosomal scaffolding proteins and rare instances of independent putative CBMs. The requirement of CBMs existing as modules within larger enzymes sets this class of carbohydrate-binding protein apart from other non-catalytic sugar binding proteins such as lectins and sugar transport proteins.

CBMs were previously classified as cellulose-binding domains (CBDs) based on the initial discovery of several modules that bound cellulose [PMID: 3338453, PMID: 3134347]. However, additional modules in carbohydrate-active enzymes are continually being found that bind carbohydrates other than cellulose yet otherwise meet the CBM criteria, hence the need to reclassify these polypeptides using more inclusive terminology.

Previous classification of cellulose-binding domains were based on amino acid similarity. Groupings of CBDs were called "Types" and numbered with roman numerals (e.g. Type I or Type II CBDs). In keeping with the glycoside hydrolase classification, these groupings are now called families and numbered with Arabic numerals. Families 1 to 13 are the same as Types I to XIII. For a detailed review on the structure and binding modes of CBMs see [PMID: 15214846].

This entry represents CBM20, which binds starch. The crystal structure of CBM20 has been solved [PMID: 1826034]. It consists of seven beta-stands forming an open-sided distorted beta-barrel. Several aromatic residues, especially the well-conserved Trp and Tyr residues, participate in granular starch binding.

GO terms

Biological Process

No terms assigned in this category.

Molecular Function

GO:2001070 starch binding

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE profiles