Inositol monophosphate phosphatase genes of Mycobacterium tuberculosis
1 Department of Pathology and Infectious Diseases, Royal Veterinary College, Royal College Street, London NW1 0TU, UK
2 Tuberculosis Research, Veterinary Laboratories Agency, New Haw, Addlestone, Surrey KT15 3NB, UK
3 CNRS, Institut de Pharmacologie et Biologie Structurale, UMR CNRS-Université Paul Sabatier (UMR 5089), 205, route de Narbonne, 31077 Toulouse cedex 04, France
4 Department of Medicine, Division of Infectious Diseases, University of British Columbia, 2733 Heather St., Vancouver, British Columbia, Canada V5Z 3J5
5 Queen Mary University of London, Barts and the London School of Medicine and Dentistry, 4 Newark Street, London E1 2AT, UK
6 Current address: Institute for Tuberculosis Research (M/C 964), College of Pharmacy, Rm 412, University of Illinois at Chicago, 833 S. Wood St. Chicago, Illinois USA 60612-7231
BMC Microbiology 2010, 10:50 doi:10.1186/1471-2180-10-50Published: 18 February 2010
Mycobacteria use inositol in phosphatidylinositol, for anchoring lipoarabinomannan (LAM), lipomannan (LM) and phosphatidylinosotol mannosides (PIMs) in the cell envelope, and for the production of mycothiol, which maintains the redox balance of the cell. Inositol is synthesized by conversion of glucose-6-phosphate to inositol-1-phosphate, followed by dephosphorylation by inositol monophosphate phosphatases (IMPases) to form myo-inositol. To gain insight into how Mycobacterium tuberculosis synthesises inositol we carried out genetic analysis of the four IMPase homologues that are present in the Mycobacterium tuberculosis genome.
Mutants lacking either impA (Rv1604) or suhB (Rv2701c) were isolated in the absence of exogenous inositol, and no differences in levels of PIMs, LM, LAM or mycothiol were observed. Mutagenesis of cysQ (Rv2131c) was initially unsuccessful, but was possible when a porin-like gene of Mycobacterium smegmatis was expressed, and also by gene switching in the merodiploid strain. In contrast, we could only obtain mutations in impC (Rv3137) when a second functional copy was provided in trans, even when exogenous inositol was provided. Experiments to obtain a mutant in the presence of a second copy of impC containing an active-site mutation, in the presence of porin-like gene of M. smegmatis, or in the absence of inositol 1-phosphate synthase activity, were also unsuccessful. We showed that all four genes are expressed, although at different levels, and levels of inositol phosphatase activity did not fall significantly in any of the mutants obtained.
We have shown that neither impA, suhB nor cysQ is solely responsible for inositol synthesis. In contrast, we show that impC is essential for mycobacterial growth under the conditions we used, and suggest it may be required in the early stages of mycothiol synthesis.