Structural features of antigenic determinants on variant surface glycoproteins from Trypanosoma brucei

The immunochemical structure of two variant surface glycoproteins (VSGs) from Trypanosoma brucei has been studied using monoclonal and polyclonal antibodies. These two VSGs, WaTat 1.1 and WaTat 1.12 have been shown to possess cross-reactive surface-exposed antigenic determinants [Barbet et al., Nature 300, 53-57 (1982)] and similar N-terminal amino acid sequences [Olafson et al., Molec. Biochem. Parasit. 12, 287-298 (1984)]. Monoclonal and polyclonal antibodies were raised against the soluble forms of the two VSGs and against their reduced, alkylated and cyanogen bromide (CNBr) cleaved forms. None of the monoclonal antibodies which bound to the surface of living trypanosomes bound to CNBr fragments of the VSGs nor to denatured VSGs. Polyclonal antibodies raised against denatured and cleaved VSG did not bind to the surface of the living trypanosomes. These results suggest that the variable surface exposed antigenic determinants of VSG are topographically assembled structures. It was also shown that the conserved amino terminal peptides of WaTat 1.1 and WaTat 1.12 do not contain antigenic determinants.