title: Identification of a gene involved in the biosynthesis of cyclopropanated mycolic acids in Mycobacterium tuberculosis.
abstract: Mycolic acids represent a major constituent of the mycobacterial cell wall complex, which provides the first line of defense against potentially lethal environmental conditions. Slow-growing pathogenic mycobacteria such as Mycobacterium tuberculosis modify their mycolic acids by cyclopropanation, whereas fast-growing saprophytic species such as Mycobacterium smegmatis do not, suggesting that this modification may be associated with an increase in oxidative stress experienced by the slow-growing species. We have demonstrated the transformation of the distal cis double bond in the major mycolic acid of M. smegmatis to a cis-cyclopropane ring upon introduction of cosmid DNA from M. tuberculosis. This activity was localized to a single gene (cma1) encoding a protein that was 34% identical to the cyclopropane fatty acid synthase from Escherichia coli. Adjacent regions of the DNA sequence encode open reading frames that display homology to other fatty acid biosynthetic enzymes, indicating that some of the genes required for mycolic acid biosynthesis may be clustered in this region. M. smegmatis overexpressing the cma1 gene product significantly resist killing by hydrogen peroxide, suggesting that this modification may be an important adaptation of slow-growing mycobacteria to oxidative stress.
authors.affiliation: Laboratory of Intracellular Parasites, National Institutes for Allergy and Infectious Diseases, Rocky Mountain Laboratories, Hamilton, MT 59840, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Yuan
authors.forename: R E
authors.initials: RE
authors.lastname: Lee
authors.forename: G S
authors.initials: GS
authors.lastname: Besra
authors.forename: J T
authors.initials: JT
authors.lastname: Belisle
authors.forename: C E
authors.initials: CE
authors.lastname: Barry
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D003360:Cosmids; D003521:Cyclopropanes / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D005798:Genes, Bacterial; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D008780:Methyltransferases / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D009166:Mycobacterium leprae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000235:genetics* / Q000378:metabolism*; D009171:Mycolic Acids / Q000737:chemistry / Q000378:metabolism*; D016366:Open Reading Frames; D016133:Polymerase Chain Reaction; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid
chemical_list: D003521:Cyclopropanes; D009171:Mycolic Acids; D006861:Hydrogen Peroxide; D008780:Methyltransferases; C019964:cyclopropane synthetase