title: Identification of a methyltransferase from Mycobacterium smegmatis involved in glycopeptidolipid synthesis.
abstract: Glycopeptidolipids (GPLs) are major components of the cell walls of several species of mycobacteria. We have isolated a transposon mutant of Mycobacterium smegmatis that is unable to synthesize mature GPLs and that displays a rough colony morphology. The disrupted gene, mtf1, shares a high degree of homology with several S-adenosylmethionine-dependent methyltransferases. The enzyme encoded by mtf1 is required for the methylation of a single rhamnose residue that forms part of the conserved GPL core structure. This conclusion is supported by the finding that (a) the mutant synthesized only GPLs with undermethylated (either mono- or nonmethylated instead of di- or trimethylated) rhamnose residues; (b) complementation of the mutant with a wild-type copy of mtf1 restored high levels of synthesis of GPLs containing di- and trimethylated rhamnose; and (c) S-adenosylmethionine-dependent methylation of rhamnosylated GPLs could be detected in cell lysates of wild-type cells and mtf1-complemented mutant cells, but not in mutant cells lacking intact mtf1. Structural analysis of wild-type and mutant GPLs suggests that disruption of mtf1 specifically inhibits addition of O-methyl groups to the 3 (or 2)-position of the rhamnose. In the absence of 3-O-methylation, further methylation of GPL rhamnose is apparently inhibited, and overall GPL synthesis is down-regulated by 90%.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Melbourne, Royal Parade, Parkville, Victoria 3052, Australia.
authors.forename: J H
authors.initials: JH
authors.lastname: Patterson
authors.forename: M J
authors.initials: MJ
authors.lastname: McConville
authors.forename: R E
authors.initials: RE
authors.lastname: Haites
authors.forename: R L
authors.initials: RL
authors.lastname: Coppel
authors.forename: H
authors.initials: H
authors.lastname: Billman-Jacobe
mesh_terms: D000595:Amino Acid Sequence; D002473:Cell Wall / Q000737:chemistry; D017124:Conserved Sequence; D006001:Glycoconjugates / Q000096:biosynthesis* / Q000737:chemistry / Q000302:isolation & purification; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D020102:Mycobacterium smegmatis / Q000201:enzymology* / Q000235:genetics*; D016366:Open Reading Frames; D012210:Rhamnose / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D006001:Glycoconjugates; D012436:S-Adenosylmethionine; D008780:Methyltransferases; C413028:methyltransferase Mtf1; D012210:Rhamnose