2q6v
From Proteopedia
Crystal Structure of GumK in complex with UDP
Structural highlights
FunctionGUMK_XANCE Catalyzes the transfer of a glucuronic acid (GlcA) residue from UDP-glucuronate to mannose-alpha-1,3-glucose-beta-1,4-glucose-P-P-polyisoprenyl to form the lipid-linked tetrasaccharide GlcA-Man-Glc(2)-PP-Pol, with a glucuronic acid-beta-mannose linkage. Is involved in the biosynthesis of the exopolysaccharide xanthan, since it catalyzes the fourth glycosylation step in the assembly of the pentasaccharide-P-P-polyisoprenyl repeating unit of xanthan. Is unable to use the trisaccharide acceptor freed from the pyrophosphate lipid moiety. Does not show specificity for the lipidic portion of the acceptor. Shows diminished activity when tested with 6-O-acetyl-mannose-alpha-1,3-glucose-beta-1,4-glucose-P-P-polyisoprenyl, a putative intermediate in the synthesis of xanthan; this could indicate that acetylation of the internal mannose takes place after the formation of the GumK product.[1] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedXanthomonas campestris GumK (beta-1,2-glucuronosyltransferase) is a 44-kDa membrane-associated protein that is involved in the biosynthesis of xanthan, an exopolysaccharide crucial for this bacterium's phytopathogenicity. Xanthan also has many important industrial applications. The GumK enzyme is the founding member of the glycosyltransferase family 70 of carbohydrate-active enzymes, which is composed of bacterial glycosyltransferases involved in exopolysaccharide synthesis. No x-ray structures have been reported for this family. To better understand the mechanism of action of the bacterial glycosyltransferases in this family, the x-ray crystal structure of apo-GumK was solved at 1.9 angstroms resolution. The enzyme has two well defined Rossmann domains with a catalytic cleft between them, which is a typical feature of the glycosyltransferase B superfamily. Additionally, the crystal structure of GumK complexed with UDP was solved at 2.28 angstroms resolution. We identified a number of catalytically important residues, including Asp157, which serves as the general base in the transfer reaction. Residues Met231, Met273, Glu272, Tyr292, Met306, Lys307, and Gln310 interact with UDP, and mutation of these residues affected protein activity both in vitro and in vivo. The biological and structural data reported here shed light on the molecular basis for donor and acceptor selectivity in this glycosyltransferase family. These results also provide a rationale to obtain new polysaccharides by varying residues in the conserved alpha/beta/alpha structural motif of GumK. Structure and mechanism of GumK, a membrane-associated glucuronosyltransferase.,Barreras M, Salinas SR, Abdian PL, Kampel MA, Ielpi L J Biol Chem. 2008 Sep 5;283(36):25027-35. Epub 2008 Jul 2. PMID:18596046[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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