MEP isoprenoid precursor biosynthesis

The bacterial methylerythritol phosphate (MEP/DOXP) route converts pyruvate and glyceraldehyde 3-phosphate through seven reactions into isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). DXS forms the shared branch-point metabolite DXP, Dxr commits DXP to the MEP route, IspD-IspG build HMBPP, and IspH produces the two universal five-carbon isoprenoid precursors. DXP use in thiamine or pyridoxal-phosphate biosynthesis and downstream prenyl-diphosphate elongation are outside this module.

This reusable module models the bacterial route exemplified by Pseudomonas putida KT2440 and Escherichia coli K-12. The PSEPK proteins are representative members, not a taxonomic restriction. The IspG step explicitly represents flavodoxin- and ferredoxin-coupled implementations; the PSEPK and E. coli exemplars ground the flavodoxin route, while a reviewed cyanobacterial IspG grounds the ferredoxin route. IspA, IspB, UppS, UbiX, and thiolases in broad terpenoid-pathway buckets act outside the seven-reaction precursor route. This is not a literal transcription of KEGG M00096, which also includes an IDI isomerization step; here the dual-product IspH reaction supplies both required outputs, while any later IPP/DMAPP pool balancing is kept separate.