title: Inositol monophosphate phosphatase genes of Mycobacterium tuberculosis.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Pathology and Infectious Diseases, Royal Veterinary College, Royal College Street, London NW1 0TU, UK. movahed@uic.edu
authors.forename: Farahnaz
authors.initials: F
authors.lastname: Movahedzadeh
authors.forename: Paul R
authors.initials: PR
authors.lastname: Wheeler
authors.forename: Premkumar
authors.initials: P
authors.lastname: Dinadayala
authors.forename: Yossef
authors.initials: Y
authors.lastname: Av-Gay
authors.forename: Tanya
authors.initials: T
authors.lastname: Parish
authors.forename: Mamadou
authors.initials: M
authors.lastname: Daffé
authors.forename: Neil G
authors.initials: NG
authors.lastname: Stoker
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002457:Cell Extracts / Q000737:chemistry; D019295:Computational Biology; D015870:Gene Expression; D007294:Inositol / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000201:enzymology* / Q000235:genetics*; D010716:Phosphatidylinositols / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D002457:Cell Extracts; D008070:Lipopolysaccharides; D010716:Phosphatidylinositols; C050016:lipoarabinomannan; C064351:lipomannan; C034154:phosphatidylinositol mannoside; D007294:Inositol; D010744:Phosphoric Monoester Hydrolases; C021822:myo-inositol-1 (or 4)-monophosphatase