The microbial degradation of cellulose and xylans requires several types of enzyme such as endoglucanases (EC 3.2.1.4), cellobiohydrolases (EC 3.2.1.91) (exoglucanases), or xylanases (EC 3.2.1.8) [ PUBMED:1886523 ]. Structurally, cellulases and xylanases generally consist of a catalytic domain and a conserved region of … expand

The microbial degradation of cellulose and xylans requires several types of enzyme such as endoglucanases (EC 3.2.1.4), cellobiohydrolases (EC 3.2.1.91) (exoglucanases), or xylanases (EC 3.2.1.8) [ PUBMED:1886523 ]. Structurally, cellulases and xylanases generally consist of a catalytic domain and a conserved region of ~100 amino acid residues, the carbohydrate-binding module 2 (CBM2) [ PUBMED:1812490 ]. It is found either at the N-terminal or at the C-terminal extremity of these enzymes.

CBM2 can be classified in 2 subfamilies according to substrate specificities: CBM2a which binds cellulose and CBM2b which interacts specifically with xylan. Like other CBM domains CBM2 is a β-sheet domain containing a planar face which interacts with its ligand via a hydrophobic strip of aromatic residues [ PUBMED:7766609 ]. In family 2a this hydrophobic surface consists of three tryptophan residues, which are all required for binding soluble and insoluble forms of cellulose [ PUBMED:9662439 ]. In family 2b only 2 surface-exposed tryptophans are conserved and the first one is oriented differently. It is therefore not well oriented to interact with cellulose but is ideal for binding xylan [ PUBMED:10425686 ].

This domain recognises both CBM2 subfamilies.