title: Glycosyl-sn-1,2-dimyristylphosphatidylinositol is covalently linked to Trypanosoma brucei variant surface glycoprotein.
abstract: The COOH terminus of the externally disposed variant surface glycoprotein (VSG) of the eukaryotic pathogenic protozoan Trypanosoma brucei strain 427 variant MITat 1.4 (117) is covalently linked to a novel phosphatidylinositol-containing glycolipid. This conclusion is supported by analysis of the products of nitrous acid deamination or Staphylococcus aureus phosphatidylinositol-specific phospholipase C treatment of purified membrane-form VSG. Lysis of trypanosomes is accompanied by release of soluble VSG, catalyzed by activation of an endogenous phospholipase C. The only apparent difference between membrane-form VSG and soluble VSG is the removal of sn-1,2-dimyristylglycerol. The COOH-terminal glycopeptide derived by Pronase digestion of soluble VSG was characterized by chemical modification and digestion with alkaline phosphatase. The results are consistent with the single non-N-acetylated glucosamine residue being the reducing terminus of the oligosaccharide and in a glycosidic linkage to a myo-inositol monophosphate that is probably myo-inositol 1,2-cyclic monophosphate. A partial structure for the VSG COOH-terminal moiety is presented. This structure represents a new type of eukaryotic post-translational protein modification and membrane anchor. We discuss the relevance of this structure to observations that have been made with other eukaryotic membrane proteins.
mesh_terms: D000818:Animals; D002241:Carbohydrates / Q000032:analysis; D002849:Chromatography, Gas; D008401:Gas Chromatography-Mass Spectrometry; D006017:Glycolipids / Q000378:metabolism*; D006020:Glycopeptides / Q000032:analysis; D006023:Glycoproteins / Q000302:isolation & purification / Q000378:metabolism*; D019814:Myristic Acid; D009227:Myristic Acids / Q000378:metabolism; D010446:Peptide Fragments / Q000032:analysis; D010715:Phosphatidylglycerols; D010716:Phosphatidylinositols / Q000378:metabolism*; D011402:Pronase; D011485:Protein Binding; D014316:Tritium; D014346:Trypanosoma brucei brucei / Q000378:metabolism*; D014643:Variant Surface Glycoproteins, Trypanosoma
chemical_list: D002241:Carbohydrates; D006017:Glycolipids; D006020:Glycopeptides; D006023:Glycoproteins; D009227:Myristic Acids; D010446:Peptide Fragments; D010715:Phosphatidylglycerols; D010716:Phosphatidylinositols; D014643:Variant Surface Glycoproteins, Trypanosoma; D019814:Myristic Acid; D014316:Tritium; C002773:dimyristoylphosphatidylglycerol; D011402:Pronase