The Mycobacterium tuberculosis MEP (2C-methyl-d-erythritol 4-phosphate) pathway as a new drug target

Abstract

Tuberculosis (TB) is still a major public health problem, compounded by the human immunodeficiency virus (HIV)-TB co-infection and recent emergence of multidrug-resistant (MDR) and extensively drug resistant (XDR)-TB. Novel anti-TB drugs are urgently required. In this context, the 2C-methyl-d-erythritol 4-phosphate (MEP) pathway of Mycobacterium tuberculosis has drawn attention; it is one of several pathways vital for M. tuberculosis viability and the human host lacks homologous enzymes. Thus, the MEP pathway promises bacterium-specific drug targets and the potential for identification of lead compounds unencumbered by target-based toxicity. Indeed, fosmidomycin is now known to inhibit the second step in the MEP pathway. This review describes the cardinal features of the main enzymes of the MEP pathway in M. tuberculosis and how these can be manipulated in high throughput screening campaigns in the search for new anti-infectives against TB.

Fig 1. Various isoprenoids

Examples of isoprenoid compounds. Isopentenyl diphosphate and dimethylallyl diphosphate contribute the carbon architectures. (a) Phytol, (b) β-carotene or xanthophyll, (c) menaquinone, (d) ubiquinone, and (e) prenyl phosphate.

Fig 2. The mevalonate pathway for IPP biosynthesis

This pathway is an important cellular metabolic pathway present in all higher eukaryotes and some eubacteria. DMAPP and IPP serve the repeating units for the biosynthesis of isoprenoids . Abbreviation: HMG-CoA, 3-hydroxy-3-methylglutaryl CoA; HMGR, HMG-CoA reductase.

Fig 3. The 2C-methyl-D-erythritol 4-phosphate pathway

Most eubacteria utilize this pathway for the biosynthesis of IPP and DMAPP. Abbreviations: The names of structures are in the text. DXS, 1-deoxy-D-xylulose 5-phosphate synthase; IspC, 1-deoxy-D-xylulose 5-phosphate reductoisomerase; IspD, 4-diphosphocytidyl-2C-methyl-D-erythritol synthase; IspE, 4-diphosphocytidyl-2C-methyl-D-erythritol kinase; IspF, 2C-methyl-D-erythritol 2,4-cyclodiphosphate synthase; IspG, 1-hydroxy-2-methyl-2(E)-butenyl 4-diphosphate synthase; IspH, 1-hydroxy-2-methyl-2(E)-butenyl 4-diphosphate reductase; Idi, Isopentenyl diphosphate isomerase .