Family 6 carbohydrate-binding modules display multiple b1,3-linked glucan-specific binding interfaces

• Published in: FEMS microbiology letters 2009-11, Vol.300 (1), p.48-57
• Main Authors: Correia, Marcia AS, Pires, Virginia MR, Gilbert, Harry J, Bolam, David N, Fernandes, Vania O, Alves, Victor D, Prates, Jose AM, Ferreira, Luis MA, Fontes, Carlos MGA
• Format: Article
• Language: English
• ISSN: 0378-1097
• DOI: 10.1111/j.1574-6968.2009.01764.x

AbstractNoncatalytic carbohydrate-binding modules (CBMs), which are found in a variety of carbohydrate-degrading enzymes, have been grouped into sequence-based families. CBMs, by recruiting their appended enzymes onto the surface of the target substrate, potentiate catalysis particularly against insoluble substrates. Family 6 CBMs (CBM6s) display unusual properties in that they present two potential ligand-binding sites termed clefts A and B, respectively. Cleft B is located on the concave surface of the b-sandwich fold while cleft A, the more common binding site, is formed by the loops that connect the inner and the outer b-sheets. Here, we report the biochemical properties of CBM6-1 from Cellvibrio mixtus CmCel5A. The data reveal that CBM6-1 specifically recognizes b1,3-glucans through residues located both in cleft A and in cleft B. In contrast, a previous report showed that a CBM6 derived from a Bacillus halodurans laminarinase binds to b1,3-glucans only in cleft A. These studies reveal a different mechanism by which a highly conserved protein platform can recognize b1,3-glucans.