UDP-L-arabinose Biosynthesis II (from L-arabinose) …
24/08/2017 · For UDP-arabinose biosynthesis, UXE ..
In a separate but related project, we have been pursuing the identification and characterization of nucleotide sugar interconversion enzymes, which generate the donor substrates for glycosyltransferases in plant cell wall synthesis. We recently reported the molecular cloning and biochemical characterization of a Golgi-localized UDP-D-xylose 4-epimerase in the synthesis of UDP-L-arabinose, and a bifunctional UDP-sugar synthase that catalyzes the formation of the branched-chain sugar D-apiose. Our current work focuses on the characterization of plant enzymes in the the de novo synthesis of UDP-D-galacturonate and UDP-L-rhamnose, which are important precursors for the synthesis of pectic polysaccharides.
Biosynthesis of UDP-xylose and UDP-arabinose in Sinorhizobium ..
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.