Structural characterisation of nucleotide sugar short-chain dehydrogenases/reductases from the thermophilic pseudomurein-containing methanogen Methanothermobacter thermautotrophicus ΔH

Abstract

Epimerases and dehydratases are widely studied members of the extendedshort-chain dehydrogenase/reductase (SDR) enzyme superfamily and areimportant in nucleotide sugar conversion and diversification, for example,the interconversion of uridine diphosphate (UDP)-linked glucose andgalactose. Methanothermobacter thermautotrophicus contains a cluster ofgenes, the annotations of which indicate involvement in glycan biosynthesissuch as that of cell walls or capsular polysaccharides. In particular, genesencoding UDP-glucose 4-epimerase related protein (Mth375), UDP-glucose4-epimerase homologue (Mth380) and dTDP-glucose 4,6-dehydrataserelated protein (Mth373) may be involved in the biosynthesis of an unusualaminosugar in pseudomurein. In this paper, we present the structures ofMth375, an archaeal sugar epimerase/dehydratase protein (WbmF) deter-mined to a resolution of 2.0 A. The structure contains an N-terminalRossmann-fold domain with bound nicotinamide adenine dinucleotidehydride (NADH) and a C-terminal catalytic domain with bound UDP. Wealso present the structure for Mth373 co-crystallised with uridine-50-diphosphate-xylopyranose to a resolution of 1.96 A as a NAD+-dependentoxidative decarboxylase (UDP-xylose synthase; EC4.1.1.35). Molecularmodelling has also allowed for the identification of Mth380 as aUDP-N-acetylglucosamine 4-epimerase (WbpP; EC5.1.3.7), Mth631 as aUDP-glucose 4-epimerase (GalE; EC5.1.3.2) and Mth1789 as a classicaldTDP-D-glucose 4,6-dehydratase (EC4.2.1.46). The UDP–sugar specificityof each archaeal nucleotide sugar short-chain dehydrogenase/reductase.