title: The glycosylphosphatidylinositol (GPI) biosynthetic pathway of bloodstream-form Trypanosoma brucei is dependent on the de novo synthesis of inositol.
abstract: In bloodstream-form Trypanosoma brucei (the causative agent of African sleeping sickness) the glycosylphosphatidylinositol (GPI) anchor biosynthetic pathway has been validated genetically and chemically as a drug target. The conundrum that GPI anchors could not be in vivo labelled with [3H]-inositol led us to hypothesize that de novo synthesis was responsible for supplying myo-inositol for phosphatidylinositol (PI) destined for GPI synthesis. The rate-limiting step of the de novo synthesis is the isomerization of glucose 6-phosphate to 1-D-myo-inositol-3-phosphate, catalysed by a 1-D-myo-inositol-3-phosphate synthase (INO1). When grown under non-permissive conditions, a conditional double knockout demonstrated that INO1 is an essential gene in bloodstream-form T. brucei. It also showed that the de novo synthesized myo-inositol is utilized to form PI, which is preferentially used in GPI biosynthesis. We also show for the first time that extracellular myo-inositol can in fact be used in GPI formation although to a limited extent. Despite this, extracellular inositol cannot compensate for the deletion of INO1. Supporting these results, there was no change in PI levels in the conditional double knockout cells grown under non-permissive conditions, showing that perturbation of growth is due to a specific lack of de novo synthesized myo-inositol and not a general inositol-less death. These results suggest that there is a distinction between de novo synthesized myo-inositol and that from the extracellular environment.
authors.affiliation: Division of Biological Chemistry and Molecular Microbiology, The School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK.
authors.forename: Kirstee L
authors.initials: KL
authors.lastname: Martin
authors.forename: Terry K
authors.initials: TK
authors.lastname: Smith
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D015139:Blotting, Southern; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D008401:Gas Chromatography-Mass Spectrometry; D017353:Gene Deletion; D017261:Glycosylphosphatidylinositols / Q000096:biosynthesis* / Q000378:metabolism; D007294:Inositol / Q000096:biosynthesis* / Q000378:metabolism; D008969:Molecular Sequence Data; D007296:Myo-Inositol-1-Phosphate Synthase / Q000235:genetics* / Q000378:metabolism; D010716:Phosphatidylinositols / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology; D010802:Phylogeny; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D014346:Trypanosoma brucei brucei / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism
chemical_list: D017261:Glycosylphosphatidylinositols; D010716:Phosphatidylinositols; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D007294:Inositol; D007296:Myo-Inositol-1-Phosphate Synthase