Structural comparisons between the soluble and the GPI-anchored forms of the Paramecium temperature-specific 156G surface antigen. |
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Authors: | N Azzouz Y Capdeville |
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Institution: | Centre de Génétique Moléculaire, Associé à l'Université Pierre-et-Marie-Curie, Gif-sur-Yvette, France. |
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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. |
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Keywords: | GPI-protein biosynthetic labelling phosphatidylinositol-specific phospholipase C Paramecium |
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