title: The ppm operon is essential for acylation and glycosylation of lipoproteins in Corynebacterium glutamicum.
abstract: BACKGROUND
  Due to their contribution to bacterial virulence, lipoproteins and members of the lipoprotein biogenesis pathway represent potent drug targets. Following translocation across the inner membrane, lipoprotein precursors are acylated by lipoprotein diacylglycerol transferase (Lgt), cleaved off their signal peptides by lipoprotein signal peptidase (Lsp) and, in Gram-negative bacteria, further triacylated by lipoprotein N-acyl transferase (Lnt). The existence of an active apolipoprotein N-acyltransferase (Ms-Ppm2) involved in the N-acylation of LppX was recently reported in M. smegmatis. Ms-Ppm2 is part of the ppm operon in which Ppm1, a polyprenol-monophosphomannose synthase, has been shown to be essential in lipoglycans synthesis but whose function in lipoprotein biosynthesis is completely unknown.
  
  
  RESULTS
  In order to clarify the role of the ppm operon in lipoprotein biosynthesis, we investigated the post-translational modifications of two model lipoproteins (AmyE and LppX) in C. glutamicum Δppm1 and Δppm2 mutants. Our results show that both proteins are anchored into the membrane and that their N-termini are N-acylated by Cg-Ppm2. The acylated N-terminal peptide of LppX was also found to be modified by hexose moieties. This O-glycosylation is localized in the N-terminal peptide of LppX and disappeared in the Δppm1 mutant. While compromised in the absence of Cg-Ppm2, LppX O-glycosylation could be restored when Cg-Ppm1, Cg-Ppm2 or the homologous Mt-Ppm1 of M. tuberculosis was overexpressed.
  
  
  CONCLUSIONS
  Together, these results show for the first time that Cg-Ppm1 (Ppm synthase) and Cg-Ppm2 (Lnt) operate in a common biosynthetic pathway in which lipoprotein N-acylation and glycosylation are tightly coupled.
authors.affiliation: Institut de Biochimie et de Biophysique Moléculaire et Cellulaire, Université Paris-Sud, Orsay, France.
authors.forename: Niloofar
authors.initials: N
authors.lastname: Mohiman
authors.forename: Manuela
authors.initials: M
authors.lastname: Argentini
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Batt
authors.forename: David
authors.initials: D
authors.lastname: Cornu
authors.forename: Muriel
authors.initials: M
authors.lastname: Masi
authors.forename: Lothar
authors.initials: L
authors.lastname: Eggeling
authors.forename: Gurdyal
authors.initials: G
authors.lastname: Besra
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bayan
mesh_terms: D000215:Acylation; D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002853:Chromatography, Liquid; D048230:Corynebacterium glutamicum / Q000201:enzymology / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D006031:Glycosylation; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000201:enzymology / Q000235:genetics; D009876:Operon; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D001426:Bacterial Proteins; D007527:Isoenzymes; D008074:Lipoproteins; D011994:Recombinant Proteins; D000217:Acyltransferases; C068902:apolipoprotein N-acyltransferase