title: The biosynthesis of L-arabinose in plants: molecular cloning and characterization of a Golgi-localized UDP-D-xylose 4-epimerase encoded by the MUR4 gene of Arabidopsis.
abstract: The mur4 mutant of Arabidopsis shows a 50% reduction in the monosaccharide L-Ara in leaf-derived cell wall material because of a partial defect in the 4-epimerization of UDP-D-Xyl to UDP-L-Ara. To determine the genetic lesion underlying the mur4 phenotype, the MUR4 gene was cloned by a map-based procedure and found to encode a type-II membrane protein with sequence similarity to UDP-D-Glc 4-epimerases. Enzyme assays of MUR4 protein expressed in the methylotropic yeast Pichia pastoris indicate that it catalyzes the 4-epimerization of UDP-D-Xyl to UDP-L-Ara, the nucleotide sugar used by glycosyltransferases in the arabinosylation of cell wall polysaccharides and wall-resident proteoglycans. Expression of MUR4-green fluorescent protein constructs in Arabidopsis revealed localization patterns consistent with targeting to the Golgi, suggesting that the MUR4 protein colocalizes with glycosyltransferases in the biosynthesis of arabinosylated cell wall components. The Arabidopsis genome encodes three putative proteins with >76% sequence identity to MUR4, which may explain why mur4 plants are not entirely deficient in the de novo synthesis of UDP-L-Ara.
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269, USA.
authors.forename: Emilie G
authors.initials: EG
authors.lastname: Burget
authors.forename: Rajeev
authors.initials: R
authors.lastname: Verma
authors.forename: Michael
authors.initials: M
authors.lastname: Mølhøj
authors.forename: Wolf-Dieter
authors.initials: WD
authors.lastname: Reiter
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001089:Arabinose / Q000096:biosynthesis* / Q000737:chemistry; D002238:Carbohydrate Epimerases / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D006056:Golgi Apparatus / Q000201:enzymology*; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010843:Pichia / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D001089:Arabinose; D002238:Carbohydrate Epimerases; C474210:MUR4 protein, Arabidopsis