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.

Scope and generalization: the RmlABCD route is conserved across Bacteria (Proteobacteria, Firmicutes, Actinobacteria, Cyanobacteria and others) and RmlC/RmlD homologs occur in some archaea, so the module is written species-neutrally and grounded to PANTHER families and bacterial PAINT nodes, with E. coli K-12 (experimentally characterised RfbA; rfb O16 cluster) and P. putida KT2440 (PP_1782-PP_1785 rfbC-rfbA-rfbD-rffG cluster plus the extra RmlC paralog PP_0265) as exemplars. Plants make UDP-L-rhamnose with trifunctional RHM enzymes instead and are outside this module. Representative members are exemplars, not simultaneously required pathway components. The KT2440 RmlD-like paralog PP_0500 lacks the NCBIfam TIGR01214 rmlD model and has no established substrate, so it is not used as an exemplar. Downstream O-antigen, LPS, capsule and secondary-metabolite assembly are product-use context outside the module boundary; the member gene reviews mark propagated polymer-level process terms (polysaccharide, LPS and O-antigen biosynthesis) as over-annotations of these precursor-supply enzymes. Location (cytosol, accepted on every member review) is omitted from this reusable reaction module because it adds no pathway discrimination. Family-function QC: PTHR43000 is a heterogeneous NAD(P)-dependent epimerase/dehydratase superfamily whose review leaves GO:0008460 UNRESOLVED at family scope while assessing the bacterial RmlB/RffG node PTN000042046 as SOUND, so the module keeps the verified PANTHER id for membership and cites that node; the resulting FAMILY_FUNCTION_UNREVIEWED warning is expected.