title: Giardia duodenalis: direct experimental evidence for the absence of a glycosylphosphatidylinositol anchor in a variant surface protein.
abstract: The trophozoites of Giardia duodenalis express variant surface proteins (VSPs) that cover the entire surface of the cell and can be altered by antigenic variation. In the present study, a VSP (VSPH7) expressed by the Giardia GS isolate was purified using Triton-X-114 extraction/phase partitioning and a combination of column chromatography methods. The purified VSP was typed by mass spectrometric fingerprint mapping and peptide sequencing and found to share 58-99.8% peptide identity with the VSPH7 protein sequence previously deduced from the cloned cDNA. Carbohydrate compositional analyses consistently showed the presence of galactose in the VSP preparations but a direct association of carbohydrate with the VSPH7 could not be established. Analysis of the C-terminal part of the purified VSPH7 by off-blot myo-inositol analysis provided for the first time direct experimental evidence that this protein is not modified via a GPI lipid.
authors.affiliation: Institute of Parasitology, University of Zurich, Winterthurerstrasse 266a, 8057 Zurich, Switzerland.
authors.forename: Andreas J
authors.initials: AJ
authors.lastname: Hülsmeier
authors.forename: Peter
authors.initials: P
authors.lastname: Köhler
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000940:Antigenic Variation; D000953:Antigens, Protozoan / Q000737:chemistry* / Q000276:immunology; D015153:Blotting, Western; D002469:Cell Separation; D002848:Chromatography, DEAE-Cellulose; D004591:Electrophoresis, Polyacrylamide Gel; D005434:Flow Cytometry; D008401:Gas Chromatography-Mass Spectrometry; D016829:Giardia lamblia / Q000737:chemistry* / Q000276:immunology; D017261:Glycosylphosphatidylinositols / Q000737:chemistry*; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D015800:Protozoan Proteins / Q000737:chemistry* / Q000276:immunology; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D000953:Antigens, Protozoan; D017261:Glycosylphosphatidylinositols; D015800:Protozoan Proteins; C072464:variant surface protein H7, Giardia lamblia