title: Structural and Functional Characterization of a Novel Family GH115 4-O-Methyl-α-Glucuronidase with Specificity for Decorated Arabinogalactans.
abstract: Glycoside hydrolases are clustered into families based on amino acid sequence similarities, and belonging to a particular family can infer biological activity of an enzyme. Family GH115 contains α-glucuronidases where several members have been shown to hydrolyze terminal α-1,2-linked glucuronic acid and 4-O-methylated glucuronic acid from the plant cell wall polysaccharide glucuronoxylan. Other GH115 enzymes show no activity on glucuronoxylan, and therefore, it has been proposed that family GH115 may be a poly-specific family. In this study, we reveal that a putative periplasmic GH115 from the human gut symbiont Bacteroides thetaiotaomicron, BtGH115A, hydrolyzes terminal 4-O-methyl-glucuronic acid residues from decorated arabinogalactan isolated from acacia tree. The three-dimensional structure of BtGH115A reveals that BtGH115A has the same domain architecture as the other structurally characterized member of this family, BoAgu115A; however the position of the C-terminal module is altered with respect to each individual enzyme. Phylogenetic analysis of GH115 amino sequences divides the family into distinct clades that may distinguish different substrate specificities. Finally, we show that BtGH115A α-glucuronidase activity is necessary for the sequential digestion of branched galactans from acacia gum by a galactan-β-1,3-galactosidase from family GH43; however, while B. thetaiotaomicron grows on larch wood arabinogalactan, the bacterium is not able to metabolize acacia gum arabinogalactan, suggesting that BtGH115A is involved in degradation of arabinogalactan fragments liberated by other microbial species in the gastrointestinal tract.
authors.affiliation: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747AG Groningen, The Netherlands.
authors.forename: Friso
authors.initials: F
authors.lastname: Aalbers
authors.affiliation: York Structural Biology Laboratory, Department of Chemistry, University of York, YO10 5DD, York, United Kingdom.
authors.forename: Johan P
authors.initials: JP
authors.lastname: Turkenburg
authors.affiliation: York Structural Biology Laboratory, Department of Chemistry, University of York, YO10 5DD, York, United Kingdom.
authors.forename: Gideon J
authors.initials: GJ
authors.lastname: Davies
authors.affiliation: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747AG Groningen, The Netherlands.
authors.forename: Lubbert
authors.initials: L
authors.lastname: Dijkhuizen
authors.affiliation: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747AG Groningen, The Netherlands; York Structural Biology Laboratory, Department of Chemistry, University of York, YO10 5DD, York, United Kingdom. Electronic address: a.lammerts.van.bueren@rug.nl.
authors.forename: Alicia
authors.initials: A
authors.lastname: Lammerts van Bueren
mesh_terms: D000595:Amino Acid Sequence; D001439:Bacteroides / Q000201:enzymology*; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D005685:Galactans / Q000737:chemistry*; D041981:Gastrointestinal Tract / Q000382:microbiology; D006026:Glycoside Hydrolases / Q000737:chemistry*; D006170:Gum Arabic / Q000737:chemistry; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D033903:Periplasmic Proteins / Q000737:chemistry*; D010802:Phylogeny; D013379:Substrate Specificity
chemical_list: D005685:Galactans; D033903:Periplasmic Proteins; D006170:Gum Arabic; D006026:Glycoside Hydrolases; C096734:alpha-glucuronidase; C005653:arabinogalactan
keywords: carbohydrate metabolism; glycoside hydrolase; kinetics; phylogeny; structure