Biosynthesis of UDP--l-Arabinofuranoside for the Capsular Polysaccharides of Campylobacter jejuni.
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Campylobacter jejuni is the leading cause of food poisoning in North America and Europe. The exterior surface of this bacterium is coated with a capsular polysaccharide (CPS) which enables adherence to the host epithelial cells and evasion of the host immune system. Many strains of C. jejuni can be differentiated from one another by changes in the sequence of the carbohydrates found within the CPS. The CPS structures of serotypes HS:15 and HS:41 of C. jejuni were chemically characterized and found to contain an l-arabinofuranoside moiety in the repeating CPS sequence. Sequence similarity and genome neighborhood networks were used to identify the putative gene cluster within the HS:15 serotype for the biosynthesis of the l-arabinofuranoside fragment. The first enzyme (HS:15.18) in the pathway was found to catalyze the NAD+-dependent oxidation of UDP--d-glucose to UDP--d-glucuronate, while the second enzyme (HS:15.19) catalyzes the NAD+-dependent decarboxylation of this product to form UDP--d-xylose. The UDP--d-xylose is then epimerized at C4 by the third enzyme (HS:15.17) to produce UDP--l-arabinopyranoside. In the last step, HS:15.16 catalyzes the FADH2-dependent conversion of UDP--l-arabinopyranoside into UDP--l-arabinofuranoside. The UDP--l-arabinopyranoside mutase catalyzed reaction was further interrogated by measurement of a positional isotope exchange reaction within [18O]-UDP--l-arabinopyranoside.
