title: Lipid metabolism in Trypanosoma brucei: utilization of myristate and myristoyllysophosphatidylcholine for myristoylation of glycosyl phosphatidylinositols.
abstract: Myristate is the exclusive fatty acid species in the glycosyl phosphatidylinositol (GPI) anchor of the Trypanosoma brucei variant surface glycoprotein (VSG). [3H]Myristate can be incorporated into T. brucei GPIs by two distinct processes known as fatty acid remodelling and myristate exchange. Myristoyllysophosphatidylcholine (M-LPC) can also serve as a myristate donor for VSG in trypanosomes [Bowes, Samad, Jiang, Weaver and Mellors (1993) J. Biol. Chem. 268, 13885-13892]. We have studied in detail the myristoylation of GPIs using a [3H]M-LPC substrate. Labelling of VSG and free GPIs by [3H]M-LPC in cultured trypanosomes occurred at the same rate as with [3H]myristate. Concurrent with GPI labelling, there was rapid hydrolysis of [3H]M-LPC to generate extracellular [3H]myristate. Experiments in a trypanosomal cell-free system indicated that GPI labelling by fatty acid remodelling and myristate exchange was also equally efficient with [3H]M-LPC and [3H]myristate. Furthermore, both ATP and CoA are required for the myristoylation of GPIs by [3H]M-LPC. These experiments suggest that GPI myristoylation from M-LPC involves hydrolysis of M-LPC to free myristate. To address the physiological importance of myristate and M-LPC in VSG myristoylation, we radiolabelled trypanosomes in vivo with both substrates in medium containing serum, and found that [3H]myristate labelled VSG and GPIs more efficiently. Thus, VSG myristoylation by free myristate may be favoured in bloodstream trypanosome infections.
authors.affiliation: Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, U.S.A.
authors.forename: K A
authors.initials: KA
authors.lastname: Werbovetz
authors.forename: P T
authors.initials: PT
authors.lastname: Englund
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003065:Coenzyme A / Q000378:metabolism; D003470:Culture Media; D017261:Glycosylphosphatidylinositols / Q000096:biosynthesis* / Q000302:isolation & purification; D007700:Kinetics; D008244:Lysophosphatidylcholines / Q000378:metabolism*; D008954:Models, Biological; D019814:Myristic Acid; D009227:Myristic Acids / Q000378:metabolism*; D011865:Radioisotope Dilution Technique; D014316:Tritium; D014346:Trypanosoma brucei brucei / Q000378:metabolism*; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000096:biosynthesis
chemical_list: D003470:Culture Media; D017261:Glycosylphosphatidylinositols; D008244:Lysophosphatidylcholines; D009227:Myristic Acids; D014643:Variant Surface Glycoproteins, Trypanosoma; D019814:Myristic Acid; D014316:Tritium; C035255:myristoyllysophosphatidylcholine; D000255:Adenosine Triphosphate; D003065:Coenzyme A