title: The structure and function of an arabinan-specific alpha-1,2-arabinofuranosidase identified from screening the activities of bacterial GH43 glycoside hydrolases.
abstract: Reflecting the diverse chemistry of plant cell walls, microorganisms that degrade these composite structures synthesize an array of glycoside hydrolases. These enzymes are organized into sequence-, mechanism-, and structure-based families. Genomic data have shown that several organisms that degrade the plant cell wall contain a large number of genes encoding family 43 (GH43) glycoside hydrolases. Here we report the biochemical properties of the GH43 enzymes of a saprophytic soil bacterium, Cellvibrio japonicus, and a human colonic symbiont, Bacteroides thetaiotaomicron. The data show that C. japonicus uses predominantly exo-acting enzymes to degrade arabinan into arabinose, whereas B. thetaiotaomicron deploys a combination of endo- and side chain-cleaving glycoside hydrolases. Both organisms, however, utilize an arabinan-specific α-1,2-arabinofuranosidase in the degradative process, an activity that has not previously been reported. The enzyme can cleave α-1,2-arabinofuranose decorations in single or double substitutions, the latter being recalcitrant to the action of other arabinofuranosidases. The crystal structure of the C. japonicus arabinan-specific α-1,2-arabinofuranosidase, CjAbf43A, displays a five-bladed β-propeller fold. The specificity of the enzyme for arabinan is conferred by a surface cleft that is complementary to the helical backbone of the polysaccharide. The specificity of CjAbf43A for α-1,2-l-arabinofuranose side chains is conferred by a polar residue that orientates the arabinan backbone such that O2 arabinose decorations are directed into the active site pocket. A shelflike structure adjacent to the active site pocket accommodates O3 arabinose side chains, explaining how the enzyme can target O2 linkages that are components of single or double substitutions.
authors.affiliation: Institute for Cell and Molecular Biosciences, Newcastle University, The Medical School, Newcastle upon Tyne NE2 4HH, United Kingdom.
authors.forename: Alan
authors.initials: A
authors.lastname: Cartmell
authors.forename: Lauren S
authors.initials: LS
authors.lastname: McKee
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Peña
authors.forename: Johan
authors.initials: J
authors.lastname: Larsbrink
authors.forename: Harry
authors.initials: H
authors.lastname: Brumer
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kaneko
authors.forename: Hitomi
authors.initials: H
authors.lastname: Ichinose
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lewis
authors.forename: Anders
authors.initials: A
authors.lastname: Viksø-Nielsen
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Gilbert
authors.forename: Jon
authors.initials: J
authors.lastname: Marles-Wright
mesh_terms: D001089:Arabinose / Q000031:analogs & derivatives / Q000378:metabolism; D001439:Bacteroides / Q000201:enzymology*; D020134:Catalytic Domain; D020633:Cellvibrio / Q000201:enzymology*; D003106:Colon / Q000382:microbiology; D018360:Crystallography, X-Ray; D006026:Glycoside Hydrolases / Q000737:chemistry*; D006801:Humans
chemical_list: C431714:arabinofuranose; D001089:Arabinose; D006026:Glycoside Hydrolases