Purification, Enzymatic Characterization, and Inhibition of theZ-Farnesyl Diphosphate Synthase fromMycobacterium tuberculosis
We have recently shown that open reading frame Rv1086 of theMycobacterium tuberculosisH37Rv genome sequence encodes a unique isoprenyl diphosphate synthase. The product of this enzyme,ω,E,Z-farnesyl diphosphate, is an intermediate for the synthesis of decaprenyl phosphate, which has a central role in the biosynthesis of most features of the mycobacterial cell wall, including peptidoglycan, arabinan, linker unit galactan, and lipoarabinomannan. We have now purifiedZ-farnesyl diphosphate synthase to near homogeneity using a novel mycobacterial expression system.Z-Farnesyl diphosphate synthase catalyzed the addition of isopentenyl diphosphate toω,E-geranyl diphosphate orω,Z-neryl diphosphate yieldingω,E,Z-farnesyl diphosphate andω,Z,Z-farnesyl diphosphate, respectively. The enzyme has an absolute requirement for a divalent cation, an optimal pH range of 7–8, andKmvalues of 124 μmfor isopentenyl diphosphate, 38 μmfor geranyl diphosphate, and 16 μmfor neryl diphosphate. Inhibitors of theZ-farnesyl diphosphate synthase were designed and chemically synthesized as stable analogs ofω,E-geranyl diphosphate in which the labile diphosphate moiety was replaced with stable moieties. Studies with these compounds revealed that the active site ofZ-farnesyl diphosphate synthase differs substantially fromE-farnesyl diphosphate synthase from pig brain (Sus scrofa).