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Publication Abstract from PubMed

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 has 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, while B. thetaiotaomicron deploys a combination of endo and side chain-cleaving glycoside hydrolases. Both organisms, however, utilize an arabinan-specific alpha-1,2-arabinofuranosidase in the degradative process, an activity that has not previously been reported. The enzyme can cleave alpha-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 alpha-1,2-arabinofuranosidase, CjAbf43A displays a 5-bladed beta-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 alpha-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 shelf-like 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.

The structure and function of an arabinan-specific alpha-1,2-arabinofuranosidase identified from screening the activities of bacterial GH43 glycoside hydrolases.,Cartmell A, McKee L, Pena MJ, Larsbrink J, Brumer H, Kaneko S, Ichinose H, Lewis RJ, Vikso-Nielsen A, Gilbert HJ, Marles-Wright J J Biol Chem. 2011 Feb 21. PMID:21339299^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.