Functional cloning and characterization of a UDP- glucuronic acid decarboxylase: the pathogenic fungus Cryptococcus neoformans elucidates UDP-xylose synthesis.
UDP-xylose is a sugar donor required for the synthesis of diverse and important glycan structures in animals, plants, fungi, and bacteria. Xylose-containing glycans are particularly abundant in plants and in the polysaccharide capsule that is the major virulence factor of the pathogenic fungus Cryptococcus neoformans. Biosynthesis of UDP-xylose is mediated by UDP-glucuronic acid decarboxylase, which converts UDP-glucuronic acid to UDP-xylose. Although this enzymatic activity was described over 40 years ago it has never been fully purified, and the gene encoding it has not been identified. We used homology to a bacterial gene, hypothesized to encode a related function, to identify a cryptococcal sequence as putatively encoding a UDP-glucuronic acid decarboxylase. A soluble 47-kDa protein derived from bacteria expressing the C. neoformans gene catalyzed conversion of UDP-glucuronic acid to UDP-xylose, as confirmed by NMR analysis. NADH, UDP, and UDP-xylose inhibit the activity. Close homologs of the cryptococcal gene, which we termed UXS1, appear in genome sequence data from organisms ranging from bacteria to humans.
Bar-Peled
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Complex Carbohydrate Research Center and Department of Botany, University of Georgia, Athens, GA 30602, USA. peled@ccrc.uga.edu
Griffith
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Doering
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D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001483:Base Sequence; D002262:Carboxy-Lyases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002413:Cations, Divalent; D003001:Cloning, Molecular; D003455:Cryptococcus neoformans / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity; D004271:DNA, Fungal; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009243:NAD / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D016366:Open Reading Frames; D013379:Substrate Specificity; D013696:Temperature; D014535:Uridine Diphosphate Glucuronic Acid / Q000378:metabolism; D014540:Uridine Diphosphate Xylose / Q000096:biosynthesis* / Q000737:chemistry
D002413:Cations, Divalent; D004271:DNA, Fungal; D009243:NAD; D014535:Uridine Diphosphate Glucuronic Acid; D014540:Uridine Diphosphate Xylose; D002262:Carboxy-Lyases; C023257:UDPglucuronate decarboxylase