FIGURE 1.

Comparative GDP-6-deoxy-d-altro-heptose and GDP-6-O-Me-l-gluco-heptose synthesis pathways of C. jejuni. The 6-deoxy-d-altro-heptose synthesis pathway shown in panel A is as established previously (24, 25). The 6-O-Me-l-gluco-heptose synthesis pathway shown in panel B is hypothetical. The C4 oxidase MlghA necessary to form the 4-keto derivative necessary for MlghB activity has not been identified. A putative methyltransferase MlghD has been identified but not characterized so that it is not currently known when the 6-O methyl group is introduced along this pathway, as indicated by the question marks. R refers to the fact that in vivo the enzymes from C. jejuni strain NCTC 11168 may use 6-O-methyl or non-methylated derivatives.