dTDP-L-rhamnose biosynthesis

Species-neutral bacterial module for synthesis of the activated sugar dTDP-L-rhamnose from alpha-D-glucose 1-phosphate. The pathway proceeds through dTDP-glucose formation, dTDP-glucose 4,6-dehydration, dTDP-4-dehydrorhamnose 3,5-epimerization, and final NADPH-dependent reduction to dTDP-L-rhamnose. The module represents the soluble nucleotide-sugar supply pathway and treats downstream O-antigen, LPS, and specialized-polysaccharide assembly reactions as consumers, not as part of the biosynthetic module itself.

The PP_1782-PP_1785 rfbC-rfbA-rfbD-rffG cluster provides a complete PSEPK implementation. PP_0265 is an additional RmlC-family epimerase; PP_0500 is an additional RmlD-family protein whose physiological substrate remains an open question. Representative members are exemplars, not simultaneously required pathway components. Downstream O-antigen and glycan assembly are product-use context outside this module boundary. PSEPK gene reviews accept cytosol for the soluble enzymes, but location is omitted from this reusable reaction module because it is not a defining constraint and repeating it on the module plus every annoton would add no pathway discrimination.