title: Structural comparisons between the soluble and the GPI-anchored forms of the Paramecium temperature-specific 156G surface antigen.
abstract: Biosynthetic labelling experiments performed on P primaurelia strain 156, expressing the temperature-specific G surface antigen, 156G SAg, demonstrated that the purified 156G SAg contained the components characteristic of a GPI-anchor. [3H]ethanolamine, [3H]myo-inositol, [32P]phosphoric acid and [3H]myristic acid could all be incorporated into the surface antigen. Myristic acid labelling was lost after treatment in vitro with Bacillus thuringiensis phosphatidylinositol-specific phospholipase C (PI-PLC). After complete digestion by pronase, a fragment containing the intact GPI-anchor of 156G surface antigen was isolated. This fragment was shown to be hydrophobic and glycosylated and to possess an epitope found specifically in the GPI component of GPI-anchored proteins. The role of the GPI-tail in anchoring the 156G surface antigen into the membrane was assessed by determining that purified 156G molecules with the GPI-anchor could be incorporated into lipid vesicles and red cell ghosts whereas the 156G molecules lacking the GPI-anchor, as result of treatment with B thuringiensis PI-PLC, could not. It has also been shown that the membrane-bound form and the soluble form, obtained after cleavage of the 156G SAg lipid moiety either by an endogenous PI-PLC or by a bacterial PI-PLC, displayed identical circular dichroic spectra.
authors.affiliation: Centre de Génétique Moléculaire, Associé à l'Université Pierre-et-Marie-Curie, Gif-sur-Yvette, France.
authors.forename: N
authors.initials: N
authors.lastname: Azzouz
authors.forename: Y
authors.initials: Y
authors.lastname: Capdeville
mesh_terms: D000818:Animals; D000953:Antigens, Protozoan / Q000737:chemistry*; D000954:Antigens, Surface / Q000737:chemistry*; D002942:Circular Dichroism; D017261:Glycosylphosphatidylinositols / Q000032:analysis; D008081:Liposomes; D008562:Membrane Glycoproteins / Q000737:chemistry*; D010247:Paramecium / Q000276:immunology*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D011487:Protein Conformation; D012995:Solubility; D013696:Temperature
chemical_list: D000953:Antigens, Protozoan; D000954:Antigens, Surface; D017261:Glycosylphosphatidylinositols; D008081:Liposomes; D008562:Membrane Glycoproteins; D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C; D043265:Phosphatidylinositol Diacylglycerol-Lyase