A study of the membrane attachment site of the membrane-form variant surface glycoprotein from Trypanosoma brucei brucei using lipid vesicles as a model of the plasma membrane.

The incorporation of the membrane form and the soluble form of variant surface glycoprotein (mfVSG and sVSG) from Trypanosoma brucei brucei into liposomes has been investigated. It was found that selective incorporation of mfVSG into liposomes was possible in the presence of 8 M urea as a denaturing agent; sVSG, by contrast, was incorporated only poorly into liposomes. After proteolysis of mfVSG incorporated into liposomes, a compound was isolated from the liposomes which carries with it constituents of the glyophospholipid membrane anchor: ethanolamine, di-14:0-diglyceride and phosphatidylinositol were identified by electron impact and fast atom bombardment mass spectrometry, thus providing direct confirmation of the earlier findings of Holder [Holder, A.A. (1983) Biochem. J. 209, 261-262] and Ferguson et al. [Ferguson, M.A.J., Haldar, K. and Cross, G.A.M. (1985) J. Biol. Chem. 260, 4963-4968; Ferguson, M.A.J., Low, M.G. and Cross, G.A.M. (1985) J. Biol. Chem. 260, 14547-14555].