title: Biosynthesis of the linkage region of the mycobacterial cell wall.
abstract: The "core" structure of the cell wall of Mycobacterium and related genera is unique among prokaryotes, consisting of a covalently linked complex of mycolic acids, D-arabinan and D-galactan (mycolylarabinogalactan, mAG), which, in turn, is linked to peptidoglycan via a special linkage unit, -alpha-L-Rhap(1-->3)-D-GlcNAc-P-. Little is known of the biosynthesis of this complex, although it is the site of action of several common anti-tuberculosis drugs. Isolated cell membranes of Mycobacterium smegmatis catalyzed the incorporation of [14C]GlcNAc from UDP-[14C]GlcNAc into two glycolipids (1 and 2) and of [14C]Rha from TDP-[14C]Rha into glycolipid 2. These products were characterized as polyprenol-P-P-GlcNAc (glycolipid 1) and polyprenol-P-P-GlcNAc-Rha (glycolipid 2) based on sensitivity of synthesis to tunicamycin, chromatographic characterization of the products of mild acid hydrolysis, and mass spectral analysis of the glycosyl and polyprenyl units. Glycolipids 1 and 2 were shown to be precursors of the linkage unit in polymerized cell wall. The inclusion in the assays of UDP-[14C]Galp and a preparation of cell walls allowed the incorporation of [14C]Gal into two further glycolipids (3 and 4). Preliminary evidence indicates a precursor-product relationship among glycolipids 1, 2, 3, and 4. Thus, the first steps in the biosynthesis of the mycobacterial cell wall involve synthesis of the linkage disaccharide on a polyprenyl-P-P carrier followed by growth of the galactan unit. Assays are thus defined for the screening of new anti-tuberculosis drugs active against cell wall synthesis.
authors.affiliation: Department of Microbiology, Colorado State University, Fort Collins, 80523, USA.
authors.forename: K
authors.initials: K
authors.lastname: Mikusová
authors.forename: M
authors.initials: M
authors.lastname: Mikus
authors.forename: G S
authors.initials: GS
authors.lastname: Besra
authors.forename: I
authors.initials: I
authors.lastname: Hancock
authors.forename: P J
authors.initials: PJ
authors.lastname: Brennan
mesh_terms: D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002250:Carbon Radioisotopes; D002473:Cell Wall / Q000378:metabolism; D002855:Chromatography, Thin Layer; D005690:Galactose / Q000378:metabolism; D007700:Kinetics; D008070:Lipopolysaccharides / Q000096:biosynthesis* / Q000737:chemistry / Q000302:isolation & purification; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009161:Mycobacterium / Q000378:metabolism*; D009844:Oligosaccharides / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D014537:Uridine Diphosphate N-Acetylglucosamine / Q000378:metabolism
chemical_list: D002250:Carbon Radioisotopes; D008070:Lipopolysaccharides; D009844:Oligosaccharides; D014537:Uridine Diphosphate N-Acetylglucosamine; D005690:Galactose