title: Biosynthesis of UDP-xylose: characterization of membrane-bound AtUxs2.
abstract: UDP-xylose (UDP-Xyl) is a sugar donor for the synthesis of glycoproteins, polysaccharides, various metabolites, and oligosaccharides in plants, vertebrates, and fungi. In plants, the biosynthesis of UDP-Xyl from UDP-glucuronic acid (UDP-GlcA) appears to be catalyzed by numerous UDP-glucuronic acid decarboxylase (Uxs) isoforms. For example, six Uxs isoforms in Arabidopsis thaliana (L.) and four in rice have been identified. However, the reason/s for the existence of several isoforms that are necessary for the synthesis of UDP-Xyl remains unknown. Here, we describe a Uxs isoform in Arabidopsis, AtUXS2, encoding an integral membrane protein that appears to be localized to the Golgi apparatus. The enzyme is a dimer and has distinct properties. Unlike the UXS3 isoform, which is shown here to be a soluble protein, the UXS2 isoform is membrane bound. The characteristics of the membrane-bound AtUxs2 and cytosolic AtUxs3 support the hypothesis that unique UDP-GlcA-DCs possessing distinct sub-cellular localizations can spatially regulate specific xylosylation events in plant cells.
authors.affiliation: Complex Carbohydrate Research Center and Department of Plant Biology, University of Georgia, 315 Riverbend Road, Athens, GA 30602-4712, USA.
authors.forename: Sivakumar
authors.initials: S
authors.lastname: Pattathil
authors.forename: April D
authors.initials: AD
authors.lastname: Harper
authors.forename: Maor
authors.initials: M
authors.lastname: Bar-Peled
mesh_terms: D017360:Arabidopsis / Q000201:enzymology*; D002262:Carboxy-Lyases / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D006056:Golgi Apparatus / Q000201:enzymology; D007425:Intracellular Membranes / Q000201:enzymology*; D007527:Isoenzymes; D014540:Uridine Diphosphate Xylose / Q000096:biosynthesis*
chemical_list: D007527:Isoenzymes; D014540:Uridine Diphosphate Xylose; D002262:Carboxy-Lyases; C023257:UDPglucuronate decarboxylase