title: The specificity of methyl transferases involved in trans mycolic acid biosynthesis in Mycobacterium tuberculosis and Mycobacterium smegmatis.
abstract: Trans mycolic acid content is directly related to cell wall fluidity and permeability in mycobacteria. Carbon-13 NMR spectroscopy of mycolic acids isolated from Mycobacterium tuberculosis (MTB) and Mycobacterium smegmatis (MSM) fed 13C-labeled precursor molecules was used to probe the biosynthetic pathways that modify mycolic acids. Heteronuclear correlation spectroscopy (HMQC) of ketomycolic acid from MTB allowed assignment of the complete 13C-NMR spectrum. Incorporation patterns from [1-13C]-acetate and [2-13C]-acetate feeding experiments suggested that the mero chain and alpha branch of mycolic acids are both synthesized by standard fatty acid biosynthetic reactions. [13C-methyl]-L-methionine was used to specifically label carbon atoms derived from the action of the methyl transferases involved in meromycolate modification. To enrich for trans mycolic acids a strain of MTB overexpressing the mma1 gene was labeled. Carbon-carbon coupling was observed in mycolate samples doubly labeled with 13C-acetate and [13C-methyl]-L-methionine and this information was used to assess positional specificity of methyl transfer. In MTB such methyl groups were found to occur exclusively on carbons derived from the 2 position of acetate, while in MSM they occurred only on carbons derived from the 1 position. These results suggest that the MSM methyltransferase MMAS-1 operates in an inverted manner to that of MTB.
authors: Tuberculosis Research Section, Laboratory of Host Defenses, National Institute of Allergy and Infectious Disease, National Institutes of Health, Twinbrook II, Room 239, 12441 Parklawn Drive, Rockville, Maryland 20852, USA.
authors: B G
authors: BG
authors: Schroeder
authors: C E
authors: CE
authors: Barry
mesh_terms: D000085:Acetates / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008780:Methyltransferases / Q000378:metabolism*; D020102:Mycobacterium smegmatis / Q000201:enzymology*; D009169:Mycobacterium tuberculosis / Q000201:enzymology*; D009171:Mycolic Acids / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000085:Acetates; D009171:Mycolic Acids; D008780:Methyltransferases