title: In vitro biosynthesis of ether-type glycolipids in the methanoarchaeon Methanothermobacter thermautotrophicus.
abstract: The biosynthesis of archaeal ether-type glycolipids was investigated in vitro using Methanothermobacter thermautotrophicus cell-free homogenates. The sole sugar moiety of glycolipids and phosphoglycolipids of the organism is the beta-D-glucosyl-(1-->6)-D-glucosyl (gentiobiosyl) unit. The enzyme activities of archaeol:UDP-glucose beta-glucosyltransferase (monoglucosylarchaeol [MGA] synthase) and MGA:UDP-glucose beta-1,6-glucosyltransferase (diglucosylarchaeol [DGA] synthase) were found in the methanoarchaeon. The synthesis of DGA is probably a two-step glucosylation: (i) archaeol + UDP-glucose --> MGA + UDP, and (ii) MGA + UDP-glucose --> DGA + UDP. Both enzymes required the addition of K(+) ions and archaetidylinositol for their activities. DGA synthase was stimulated by 10 mM MgCl(2), in contrast to MGA synthase, which did not require Mg(2+). It was likely that the activities of MGA synthesis and DGA synthesis were carried out by different proteins because of the Mg(2+) requirement and their cellular localization. MGA synthase and DGA synthase can be distinguished in cell extracts greatly enriched for each activity by demonstrating the differing Mg(2+) requirements of each enzyme. MGA synthase preferred a lipid substrate with the sn-2,3 stereostructure of the glycerol backbone on which two saturated isoprenoid chains are bound at the sn-2 and sn-3 positions. A lipid substrate with unsaturated isoprenoid chains or sn-1,2-dialkylglycerol configuration exhibited low activity. Tetraether-type caldarchaetidylinositol was also actively glucosylated by the homogenates to form monoglucosyl caldarchaetidylinositol and a small amount of diglucosyl caldarchaetidylinositol. The addition of Mg(2+) increased the formation of diglucosyl caldarchaetidylinositol. This suggested that the same enzyme set synthesized the sole sugar moiety of diether-type glycolipids and tetraether-type phosphoglycolipids.
authors.affiliation: Department of Chemistry, School of Medicine, University of Occupational and Environmental Health, Yahatanishi-ku, Kitakyushu 807-8555, Japan. h-morii@health.uoeh-u.ac.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Morii
authors.forename: Tadashi
authors.initials: T
authors.lastname: Eguchi
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Koga
mesh_terms: D019843:Archaeal Proteins / Q000378:metabolism; D002384:Catalysis / Q000187:drug effects; D005964:Glucosyltransferases / Q000378:metabolism; D005995:Glyceryl Ethers / Q000737:chemistry / Q000378:metabolism*; D006017:Glycolipids / Q000737:chemistry / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D017013:Methanobacteriaceae / Q000201:enzymology / Q000378:metabolism*; D008956:Models, Chemical; D015394:Molecular Structure; D013379:Substrate Specificity; D014532:Uridine Diphosphate Glucose / Q000378:metabolism
chemical_list: D019843:Archaeal Proteins; D005995:Glyceryl Ethers; D006017:Glycolipids; D005964:Glucosyltransferases; D008274:Magnesium; D014532:Uridine Diphosphate Glucose