title: Identification of a glycosylphosphatidylinositol anchor-modifying β1-3 galactosyltransferase in Trypanosoma brucei.
abstract: Trypanosoma brucei is the causative agent of human African sleeping sickness and the cattle disease nagana.  Trypanosoma brucei is dependent on glycoproteins for its survival and infectivity throughout its life cycle. Here we report the functional characterization of TbGT3, a glycosyltransferase expressed in the bloodstream and procyclic form of the parasite. Bloodstream and procyclic form TbGT3 conditional null mutants were created and both exhibited normal growth under permissive and nonpermissive conditions. Under nonpermissive conditions, the normal glycosylation of the major glycoprotein of bloodstream form T. brucei, the variant surface glycoprotein and the absence of major alterations in lectin binding to other glycoproteins suggested that the major function of TbGT3 occurs in the procyclic form of the parasite. Consistent with this, the major surface glycoprotein of the procyclic form, procyclin, exhibited a marked reduction in molecular weight due to changes in glycosylphosphatidylinositol (GPI) anchor side chains. Structural analysis of the mutant procyclin GPI anchors indicated that TbGT3 encodes a UDP-Gal: β-GlcNAc-GPI β1-3 Gal transferase. Despite the alterations in GPI anchor side chains, TbGT3 conditional null mutants remained infectious to tsetse flies under nonpermissive conditions.
authors.affiliation: Division of Biological Chemistry and Drug Discovery, The College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK Barcelona Centre for International Health Research, CRESIB, Hospital Clínic-Universitat de Barcelona, Barcelona 08036, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Izquierdo
authors.affiliation: Department of Parasitology Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool L3 5QA, UK.
authors.forename: Alvaro
authors.initials: A
authors.lastname: Acosta-Serrano
authors.affiliation: Division of Biological Chemistry and Drug Discovery, The College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
authors.forename: Angela
authors.initials: A
authors.lastname: Mehlert
authors.affiliation: Division of Biological Chemistry and Drug Discovery, The College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK m.a.j.ferguson@dundee.ac.uk.
authors.forename: Michael Aj
authors.initials: MA
authors.lastname: Ferguson
mesh_terms: D000818:Animals; D002236:Carbohydrate Conformation; D058851:GPI-Linked Proteins / Q000378:metabolism; D005700:Galactosyltransferases / Q000502:physiology*; D055786:Gene Knockout Techniques; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D015800:Protozoan Proteins / Q000502:physiology*; D014346:Trypanosoma brucei brucei / Q000201:enzymology* / Q000235:genetics; D014370:Tsetse Flies
chemical_list: D058851:GPI-Linked Proteins; D017261:Glycosylphosphatidylinositols; D015800:Protozoan Proteins; D005700:Galactosyltransferases
keywords: GPI-anchor; TbGT3; Trypanosoma brucei; galactosyltransferase; procyclic form