Biosynthesis of 3,6-Dideoxy-heptoses for the Capsular Polysaccharides of Campylobacter jejuni

Campylobacter jejuni is the leading cause of food poisoning in the United States. Surrounding the exterior surface of this bacterium is a capsular polysaccharide (CPS) that helps protect the organism from the host immune system. The CPS is composed of a repeating sequence of common and unusual sugar residues, including relatively rare heptoses. In the HS:5 serotype, we identified four enzymes required for the biosynthesis of GDP-3,6-dideoxy-beta-L-ribo-heptose. In the first step, GDP-D-glycero-alpha-D- manno-heptose is dehydrated to form GDP-6-deoxy-4-keto-alpha-D-lyxo-heptose. This product is then dehydrated by a pyridoxal phosphate-dependent C3-dehydratase to form GDP-3,6-dideoxy-4-keto-alpha-D-threo-heptose before being epimerized at C5 to generate GDP-3,6-dideoxy-4-keto-beta-L-erythro-heptose. In the final step, a C4-reductase uses NADPH to convert this product to GDP-3,6dideoxy-beta-L-ribo-heptose. These results are at variance with the previous report of 3,6-dideoxy-D-ribo-heptose in the CPS from serotype HS:5 of C. jejuni. We also demonstrated that GDP-3,6-dideoxy-beta-L-xylo-heptose is formed using the corresponding enzymes found in the gene cluster from serotype HS:11 of C. jejuni. The utilization of different C4-reductases from other serotypes of C. jejuni enabled the formation of GDP-3,6-dideoxy-alpha-D-arabino-heptose and GDP-3,6-dideoxy-alpha-D-lyxo-heptose.

Automated summary

Campylobacter jejuni is the main cause of food poisoning in the United States, and the capsule polysaccharide (CPS) on its surface is important for immune evasion. The biosynthesis of GDP-3,6-dideoxy-beta-L-ribo-heptose, a component of CPS, involves multiple enzymes and can vary in different serotypes of C. jejuni.