title: Parasite-specific inhibition of the glycosylphosphatidylinositol biosynthetic pathway by stereoisomeric substrate analogues.
abstract: The natural substrate for the first alpha-D-mannosyltransferase of glycosylphosphatidylinositol biosynthesis in the protozoan parasite Trypanosoma brucei is D-GlcNalpha1-6-D-myo-inositol-1-P-sn-1, 2-diacylglycerol. Here we show that a diastereoisomer, D-GlcNalpha1-6-L-myo-inositol-1-P-sn-1,2-diacylglycerol, is an inhibitor of this enzyme in a trypanosomal cell-free system. Tests with other L-myo-inositol-containing compounds revealed that L-myo-inositol-1-phosphate is the principal inhibitory component and that methylation of the 2-OH group of the L-myo-inositol residue abolishes any inhibition. Comparisons between the natural substrate and the inhibitors suggested that the inhibitors bind to the first alpha-D-mannosyltransferase by means of charge interactions with the 1-phosphate group and/or hydrogen bonds involving the 3-, 4-, and 5-OH groups of the L-myo-inositol residue, which are predicted to occupy orientations identical to those of the 1-phosphate and 5-, 4-, and 3-OH groups, respectively, of the D-myo-inositol residue of the natural substrate. However, additional experiments indicated that the 4-OH group of the D-myo-inositol residue is unlikely to be involved in substrate recognition. None of the L-myo-inositol-containing compounds that inhibited glycosylphosphatidylinositol (GPI) biosynthesis in a parasite cell-free system had any effect on GPI biosynthesis in a comparable human (HeLa) cell-free system, suggesting that other related parasite-specific inhibitors of this essential pathway might be developed.
authors.affiliation: Division of Molecular Parasitology & Biological Chemistry, Departments of Biochemistry and Chemistry, University of Dundee, Dundee DD1 5EH, Scotland, UK.
authors.forename: T K
authors.initials: TK
authors.lastname: Smith
authors.forename: M J
authors.initials: MJ
authors.lastname: Paterson
authors.forename: A
authors.initials: A
authors.lastname: Crossman
authors.forename: J S
authors.initials: JS
authors.lastname: Brimacombe
authors.forename: M A
authors.initials: MA
authors.lastname: Ferguson
mesh_terms: D000818:Animals; D002474:Cell-Free System / Q000201:enzymology / Q000469:parasitology; D004791:Enzyme Inhibitors / Q000737:chemistry; D006017:Glycolipids / Q000737:chemistry; D017261:Glycosylphosphatidylinositols / Q000037:antagonists & inhibitors* / Q000096:biosynthesis*; D006367:HeLa Cells; D006801:Humans; D007294:Inositol / Q000031:analogs & derivatives / Q000737:chemistry; D008364:Mannosyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism; D013237:Stereoisomerism; D013379:Substrate Specificity; D014346:Trypanosoma brucei brucei / Q000737:chemistry* / Q000201:enzymology* / Q000502:physiology
chemical_list: D004791:Enzyme Inhibitors; C415102:GlcNalpha1-6-myo-inositol-1-HPO4-sn-1, 2-dipalmitoylglycerol; D006017:Glycolipids; D017261:Glycosylphosphatidylinositols; D007294:Inositol; D008364:Mannosyltransferases