title: A novel family of carbohydrate-binding modules identified with Ruminococcus albus proteins.
abstract: We recently showed that some of the enzymes underpinning cellulose solubilization by Ruminococcus albus 8 lack the conventional type of dockerin module characteristic of cellulosomal proteins and instead, bear an "X" domain of unknown function at their C-termini. We have now subcloned and expressed six X domains and showed that five of them bind to xylan, chitin, microcrystalline and phosphoric-acid swollen cellulose, as well as more heterogenous substrates such as alfalfa cell walls, banana stem and wheat straw. The X domain that did not bind to these substrates was derived from a family-5 glycoside hydrolase (Cel5G), which possesses two X domains in tandem. Whereas the internal X domain failed to bind to the substrates, the recombinant dyad exhibited markedly enhanced binding relative to that observed for the C-terminal X domain alone. The evidence supports a distinctive carbohydrate-binding role of broad specificity for this type of domain, and we propose a novel family (designated family 37) of carbohydrate-binding modules that appear to be peculiar to R. albus.
authors.affiliation: Department of Molecular Microbiology and Biotechnology, Tel-Aviv University, Ramat Aviv, Israel.
authors.forename: Qi
authors.initials: Q
authors.lastname: Xu
authors.forename: Mark
authors.initials: M
authors.lastname: Morrison
authors.forename: Karen E
authors.initials: KE
authors.lastname: Nelson
authors.forename: Edward A
authors.initials: EA
authors.lastname: Bayer
authors.forename: Nof
authors.initials: N
authors.lastname: Atamna
authors.forename: Raphael
authors.initials: R
authors.lastname: Lamed
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D045857:Ruminococcus / Q000235:genetics / Q000378:metabolism*; D012995:Solubility; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D011134:Polysaccharides; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; C055213:saccharide-binding proteins; D006026:Glycoside Hydrolases