Identification of the Polymerizing Glycosyltransferase Required for the Addition of d-Glucuronic Acid to the Capsular Polysaccharide of Campylobacter jejuni.

Abstract

Campylobacter jejuni is the leading cause of food poisoning in Europe and North America. The exterior surface of this bacterium is encased by a capsular polysaccharide that is attached to a diacyl glycerol phosphate anchor via a poly-Kdo (3-deoxy-d-manno-oct-2-ulosinic acid) linker. In the HS:2 serotype of C. jejuni NCTC 11168, the repeating trisaccharide consists of d-ribose, N-acetyl-d-glucosamine, and d-glucuronate. Here, we show that the N-terminal domain of Cj1432 (residues 1-356) is responsible for the reaction of the C2 hydroxyl group from the terminal d-ribose moiety of the growing polysaccharide chain with UDP-d-glucuronate as the donor substrate. This discovery represents the first biochemical identification and functional characterization of a glycosyltransferase responsible for the polymerization of the capsular polysaccharide of C. jejuni. The product of the reaction catalyzed by the N-terminal domain of Cj1432 is the substrate for the reaction catalyzed by the C-terminal domain of Cj1438 (residues 453-776). This enzyme catalyzes amide bond formation using the C6 carboxylate of the terminal d-glucuronate moiety and (S)-serinol phosphate as substrates. It is also shown that Cj1435 catalyzes the hydrolysis of phosphate from the product catalyzed by the C-terminal domain of Cj1438. These results demonstrate that amide decoration of the d-glucuronate moiety occurs after the incorporation of this sugar into the growing polysaccharide chain.