title: Biosynthesis of mycobacterial lipoarabinomannan.
abstract: The mycobacterial lipoglycans, lipomannan (LM) and lipoarabinomannan (LAM), are potent immunomodulators in tuberculosis and leprosy. Little is known of their biosynthesis, other than being based on phosphatidylinositol (PI), and they probably originate in the phosphatidylinositol mannosides (PIMs; PIMans). A novel form of cell-free incubation involving in vitro and in situ labeling with GDP-[14C]Man of the polyprenyl-P-mannoses (C35/C50-P-Man) and the simpler PIMs of mycobacterial membranes, reisolation of the [14C]Man-labeled membranes, and in situ chase demonstrated the synthesis of a novel alpha(1-->6)-linked linear form of LM at the expense of the C35/C50-P-Man. There was little or no synthesis under these conditions of PIMan5 with its terminal alpha(1-->2)Man unit or the mature LM or LAM with copious alpha(1-->2)Man branching. Synthesis of the linear LM, but not of the simpler PIMan2, was susceptible to amphomycin, a lipopeptide antibiotic that specifically inhibits polyprenyl-P-requiring translocases. A mixture of P[3H]I and P[3H]IMan2 was incorporated into the linear LM, supporting other evidence that, like the PIMs, LM and LAM, it is a lipid-linked mannooligosaccharide and a new member of the mycobacterial glycosylphosphatidylinositol lipoglycan/glycolipid class. Hence, the simpler PIMs originate in PI and GDP-Man, but further growth of the linear backbone emanates from C35-/C50-P-Man and is amphomycin-sensitive. The origin of the alpha(1-->2)Man branches of mature PIMan5, LM, and LAM is not known at this time but is probably GDP-Man.
authors.affiliation: Department of Microbiology, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: G S
authors.initials: GS
authors.lastname: Besra
authors.forename: C B
authors.initials: CB
authors.lastname: Morehouse
authors.forename: C M
authors.initials: CM
authors.lastname: Rittner
authors.forename: C J
authors.initials: CJ
authors.lastname: Waechter
authors.forename: P J
authors.initials: PJ
authors.lastname: Brennan
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002250:Carbon Radioisotopes; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D006155:Guanosine Diphosphate Mannose / Q000378:metabolism; D055666:Lipopeptides; D008070:Lipopolysaccharides / Q000096:biosynthesis*; D008358:Mannose / Q000378:metabolism; D009161:Mycobacterium / Q000187:drug effects / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology; D011865:Radioisotope Dilution Technique; D014316:Tritium
chemical_list: D000900:Anti-Bacterial Agents; D002250:Carbon Radioisotopes; D055666:Lipopeptides; D008070:Lipopolysaccharides; D009842:Oligopeptides; C050016:lipoarabinomannan; C064351:lipomannan; D014316:Tritium; D006155:Guanosine Diphosphate Mannose; C004423:amphomycin; D008358:Mannose