The role of inositol acylation and inositol deacylation in the Toxoplasma gondii glycosylphosphatidylinositol Biosynthetic pathway

Terry K Smith, Juergen Kimmel, Nahid Azzouz, Hosam Shams-Eldin, Ralph T. Schwarz

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)

Abstract

Toxoplasma gondii is a ubiquitous parasitic protozoan that invades nucleated cells in a process thought to be in part due to several surface glycosylphosphatidylinositol (GPI)-anchored proteins, like the major surface antigenSAG1(P30), which dominates the plasma membrane. The serine protease inhibitors phenylmethylsulfonyl fluoride and diisopropyl fluoride were found to have a profound effect on the T. gondii GPI biosynthetic pathway, leading to the observation and characterization of novel inositol-acylated mannosylated GPI intermediates. This inositol acylation is acyl-CoA-dependent and takes place before mannosylation, but uniquely for this class of inositol-acyltransferase, it is inhibited by phenylmethylsulfonyl fluoride. The subsequent inositol deacylation of fully mannosylated GPI intermediates is inhibited by both phenylmethylsulfonyl fluoride and diisopropyl fluoride. The use of these serine protease inhibitors allows observations as to the timing of inositol acylation and subsequent inositol deacylation of the GPI intermediates. Inositol acylation of the non-mannosylated GPI intermediate D-GlcN alpha 1-6-D-myo-inositol-1HPO4-sn-lipid precedes mannosylation. Inositol deacylation of the fully mannosylated GPI intermediate allows further processing, i. e. addition of GalNAc side chain to the first mannose. Characterization of the phosphatidylinositol moieties present on both free GPIs and GPI-anchored proteins shows the presence of a diacylglycerol lipid, whose sn-2 position contains almost exclusively an C18: 1 acyl chain. The data presented here identify key novel inositol-acylated mannosylated intermediates, allowing the formulation of an updated T. gondii GPI biosynthetic pathway along with identification of the putative genes involved.

Original languageEnglish
Pages (from-to)32032-32042
Number of pages11
JournalJournal of Biological Chemistry
Volume282
Issue number44
DOIs
Publication statusPublished - 2 Nov 2007

Keywords

  • PHOSPHATIDYLINOSITOL MEMBRANE ANCHOR
  • VARIANT SURFACE GLYCOPROTEIN
  • MOLECULAR-WEIGHT ANTIGEN
  • TRYPANOSOMA-BRUCEI
  • PLASMODIUM-FALCIPARUM
  • AFRICAN TRYPANOSOMES
  • SUBSTRATE-SPECIFICITY
  • STRUCTURAL-ANALYSIS
  • PROTEIN ANCHORS
  • PRECURSORS

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