title: Identification of a bifunctional UDP-4-keto-pentose/UDP-xylose synthase in the plant pathogenic bacterium Ralstonia solanacearum strain GMI1000, a distinct member of the 4,6-dehydratase and decarboxylase family.
abstract: The UDP-sugar interconverting enzymes involved in UDP-GlcA metabolism are well described in eukaryotes but less is known in prokaryotes. Here we identify and characterize a gene (RsU4kpxs) from Ralstonia solanacearum str. GMI1000, which encodes a dual function enzyme not previously described. One activity is to decarboxylate UDP-glucuronic acid to UDP-beta-l-threo-pentopyranosyl-4''-ulose in the presence of NAD(+). The second activity converts UDP-beta-l-threo-pentopyranosyl-4''-ulose and NADH to UDP-xylose and NAD(+), albeit at a lower rate. Our data also suggest that following decarboxylation, there is stereospecific protonation at the C5 pro-R position. The identification of the R. solanacearum enzyme enables us to propose that the ancestral enzyme of UDP-xylose synthase and UDP-apiose/UDP-xylose synthase was diverged to two distinct enzymatic activities in early bacteria. This separation gave rise to the current UDP-xylose synthase in animal, fungus, and plant as well as to the plant Uaxs and bacterial ArnA and U4kpxs homologs.
authors.affiliation: Department of Biochemistry and Molecular Biology, and the Institute of Bioinformatics, Universityof Georgia, Complex Carbohydrate Research Center, Athens, Georgia 30602, USA.
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Gu
authors.forename: John
authors.initials: J
authors.lastname: Glushka
authors.forename: Yanbin
authors.initials: Y
authors.lastname: Yin
authors.forename: Ying
authors.initials: Y
authors.lastname: Xu
authors.forename: Timothy
authors.initials: T
authors.lastname: Denny
authors.forename: James
authors.initials: J
authors.lastname: Smith
authors.forename: Yingnan
authors.initials: Y
authors.lastname: Jiang
authors.forename: Maor
authors.initials: M
authors.lastname: Bar-Peled
mesh_terms: D000429:Alcohol Oxidoreductases / Q000737:chemistry* / Q000502:physiology; D000595:Amino Acid Sequence; D002262:Carboxy-Lyases / Q000737:chemistry* / Q000502:physiology; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000502:physiology; D010802:Phylogeny; D010944:Plants / Q000382:microbiology*; D043368:Ralstonia solanacearum / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014539:Uridine Diphosphate Sugars / Q000737:chemistry*; D014540:Uridine Diphosphate Xylose / Q000737:chemistry*
chemical_list: D009097:Multienzyme Complexes; C548538:U4kpxs protein, Ralstonia solanacearum; D014539:Uridine Diphosphate Sugars; D014540:Uridine Diphosphate Xylose; D000429:Alcohol Oxidoreductases; D002262:Carboxy-Lyases