Expression, purification and biochemical characterization of GumI, a monotopic membrane GDP-mannose:glycolipid 4-{beta}-D-mannosyltransferase from Xanthomonas campestris pv. campestris.

We describe the first biochemical characterization of the gumI gene product, an essential protein for xanthan polysaccharide synthesis. Cellular fractionation experiments reveal the presence of a protein associated with the membrane fraction, even in the absence of the other proteins responsible for the synthesis of glycolipid intermediates and the proteins involved in the polymerization and transport of the xanthan chains. By alkaline buffer extraction and detergent phase partitioning, GumI was categorized as a monotopic membrane protein.

Structure and mechanism of GumK, a membrane-associated glucuronosyltransferase.

Xanthomonas 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.

Crystallization and preliminary crystallographic characterization of GumK, a membrane-associated glucuronosyltransferase from Xanthomonas campestris required for xanthan polysaccharide synthesis.

GumK is a membrane-associated inverting glucuronosyltransferase that is part of the biosynthetic route of xanthan, an industrially important exopolysaccharide produced by Xanthomonas campestris. The enzyme catalyzes the fourth glycosylation step in the pentasaccharide-P-P-polyisoprenyl assembly, an oligosaccharide diphosphate lipid intermediate in xanthan biosynthesis. GumK has marginal homology to other glycosyltransferases (GTs).

Functional characterization of GumK, a membrane-associated beta-glucuronosyltransferase from Xanthomonas campestris required for xanthan polysaccharide synthesis.

Xanthomonas campestris is a Gram-negative bacterium that produces an exopolysaccharide known as xanthan gum. Xanthan is involved in a variety of biological functions, including pathogenesis, and is widely used in the industry as thickener and viscosifier. Although the genetics and biosynthetic process of xanthan are well documented, the enzymatic components have not been examined and no data on glycosyltransferases have been reported.