Amino terminal sequence homology among variant surface glycoproteins of African trypanosomes.

Amino terminal amino acid sequences were determined for eight variable surface glycoproteins purified from successive parasitemias of cloned Trypanosoma brucei. These sequences were compared by sequence alignment analysis with each other and with amino terminal sequences of variable surface glycoproteins from other clones of T. brucei, T. congolense and T. equiperdum. Contrary to previously held views, a remarkable degree of sequence homology was found among all sequences. In several cases the homology was greater between glycoproteins from different species than between glycoproteins isolated from successive parasite peaks, suggesting a common primordial gene for trypanosome variable surface glycoproteins. This amino terminal homology, taken together with homologies found in other regions of variant surface glycoproteins strongly suggests that their tertiary structures are conserved.