title: Family 6 carbohydrate-binding modules display multiple beta1,3-linked glucan-specific binding interfaces.
abstract: Noncatalytic 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 beta-sandwich fold while cleft A, the more common binding site, is formed by the loops that connect the inner and the outer beta-sheets. Here, we report the biochemical properties of CBM6-1 from Cellvibrio mixtus CmCel5A. The data reveal that CBM6-1 specifically recognizes beta1,3-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 beta1,3-glucans only in cleft A. These studies reveal a different mechanism by which a highly conserved protein platform can recognize beta1,3-glucans.
authors.affiliation: CIISA-Faculdade de Medicina Veterinária, Pólo Universitário do Alto da Ajuda, Avenida da Universidade Técnica, Lisboa, Portugal.
authors.forename: Márcia A S
authors.initials: MA
authors.lastname: Correia
authors.forename: Virgínia M R
authors.initials: VM
authors.lastname: Pires
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Gilbert
authors.forename: David N
authors.initials: DN
authors.lastname: Bolam
authors.forename: Vânia O
authors.initials: VO
authors.lastname: Fernandes
authors.forename: Victor D
authors.initials: VD
authors.lastname: Alves
authors.forename: José A M
authors.initials: JA
authors.lastname: Prates
authors.forename: Luís M A
authors.initials: LM
authors.lastname: Ferreira
authors.forename: Carlos M G A
authors.initials: CM
authors.lastname: Fontes
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D001665:Binding Sites; D020633:Cellvibrio / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005936:Glucans / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D011485:Protein Binding; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D005936:Glucans; D011956:Receptors, Cell Surface; C055213:saccharide-binding proteins