InterPro domain: IPR044516

This family represents UDP-glucuronic acid decarboxylases (UXS, also known as UDP-glucuronate decarboxylase or UDP-XYL synthase) which catalyse the NAD-dependent decarboxylation of UDP-glucuronic acid to form UDP-xylose, a sugar donor required for the synthesis of glycoproteins, polysaccharides, various metabolites, and oligosaccharides in plants, animals, fungi and bacteria [ 1 , 2 ]. They are members of the short-chain dehydrogenase/reductase (SDR) superfamily that also include epimerases, dehydratases, and reductases that use nucleotide-activated monosaccharides as substrates and share a Rossmann-fold NAD(P)H/NAD(P)(+) binding domain [ 3 ].

UXS proteins are primarily located in the Golgi/ER lumen, however they have also been found in the cytosol. Six isoforms have been identified in Arabidopsis: cytosolic AtUXS3/AtUXS5/AtUXS6, and AtUXS1/2/4 which have a type II transmembrane domain and located in the Golgi [ 3 , 4 ]. This distinct sub-cellular localisation may suggest specific xylosylation events are spatially regulated [ 5 , 5 ].

1. UDP-glucuronate decarboxylase, a key enzyme in proteoglycan synthesis: cloning, characterization, and localization. J. Biol. Chem. 277, 16968-75
2. UDP-glucuronic acid decarboxylases of Bacteroides fragilis and their prevalence in bacteria. J Bacteriol 193, 5252-9
3. Biosynthesis of UDP-xylose: characterization of membrane-bound AtUxs2. Planta 221, 538-48
4. Role of UDP-Glucuronic Acid Decarboxylase in Xylan Biosynthesis in Arabidopsis. Mol Plant 9, 1119-1131
5. Biosynthesis of UDP-xylose. Cloning and characterization of a novel Arabidopsis gene family, UXS, encoding soluble and putative membrane-bound UDP-glucuronic acid decarboxylase isoforms. Plant Physiol 130, 2188-98