Antigenic variation and the surface glycoproteins of Trypanosoma congolense.

Two Trypanosoma congolense variant-specific glycoproteins, which are expressed sequentially during a relapsing infection, have been purified. The proteins, termed VSG-1 and VSG-2, both have a molecular weight of 53,000 as determined by SDS polyacrylamide electrophoresis. When either antigen is electrophoresed through a pH gradient on an isoelectric focusing (IEF) gel, it gives a characteristic spectrotype of three bands. The IEF components of each VSG are antigenically similar to each other but not identical. The components of VSG-1 are immunologically distinct from the components of VSG-2, as shown by lack of cross-reactivity. The three spectrotypes may reflect microheterogeneity in amino acid sequence among the components. Both VSG-1 and VSG-2 are selectively cleaved by trypsin near their carboxy-terminal ends, indicating the existence of a possible common VSG region. Significant homology in the aminoterminal amino acid sequences of VSG-1 and VSG-2 suggests that sequentially reduplicated genes are sequentially expressed by trypanosomes during relapsing infections.