The reductase that catalyzes mycolic motif synthesis is required for efficient attachment of mycolic acids to arabinogalactan.
Mycolic acids are essential components of the cell walls of bacteria belonging to the suborder Corynebacterineae, including the important human pathogens Mycobacterium tuberculosis and Mycobacterium leprae. Mycolic acid biosynthesis is complex and the target of several frontline antimycobacterial drugs. The condensation of two fatty acids to form a 2-alkyl-3-keto mycolate precursor and the subsequent reduction of this precursor represent two key and highly conserved steps in this pathway. Although the enzyme catalyzing the condensation step has recently been identified, little is known about the putative reductase. Using an extensive bioinformatic comparison of the genomes of M. tuberculosis and Corynebacterium glutamicum, we identified NCgl2385, the orthologue of Rv2509 in M. tuberculosis, as a potential reductase candidate. Deletion of the gene in C. glutamicum resulted in a slow growing strain that was deficient in arabinogalactan-linked mycolates and synthesized abnormal forms of the mycolate-containing glycolipids trehalose dicorynomycolate and trehalose monocorynomycolate. Analysis of the native and acetylated trehalose glycolipids by MALDI-TOF mass spectrometry indicated that these novel glycolipids contained an unreduced beta-keto ester. This was confirmed by analysis of sodium borodeuteride-reduced mycolic acids by gas chromatography mass spectrometry. Reintroduction of the NCgl2385 gene into the mutant restored the transfer of mature mycolic acids to both the trehalose glycolipids and cell wall arabinogalactan. These data indicate that NCgl2385, which we have designated CmrA, is essential for the production of mature trehalose mycolates and subsequent covalent attachment of mycolic acids onto the cell wall, thus representing a focus for future structural and pathogenicity studies.
Lea-Smith
David J
DJ
Australian Research Council Centre of Excellence in Structural and Functional Microbial Genomics, and Victorian Bioinformatics Consortium, Department of Microbiology, Monash University, Clayton, Victoria 3800, Australia.
Pyke
James S
JS
Tull
Dedreia
D
McConville
Malcolm J
MJ
Coppel
Ross L
RL
Crellin
Paul K
PK
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002384:Catalysis; D002473:Cell Wall / Q000378:metabolism; D017124:Conserved Sequence; D003352:Corynebacterium / Q000378:metabolism; D048230:Corynebacterium glutamicum / Q000235:genetics / Q000378:metabolism; D005685:Galactans / Q000378:metabolism*; D006017:Glycolipids / Q000737:chemistry / Q000378:metabolism; D050296:Microbial Viability; D009154:Mutation / Q000235:genetics; D009169:Mycobacterium tuberculosis / Q000378:metabolism; D009171:Mycolic Acids / Q000378:metabolism*; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D016415:Sequence Alignment; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D001426:Bacterial Proteins; D005685:Galactans; D006017:Glycolipids; D009171:Mycolic Acids; D010088:Oxidoreductases; C005653:arabinogalactan