Purification of Trypanosoma brucei variable surface glycoproteins: analysis of degradation occurring during isolation.

Trypanosoma brucei variable surface glycoproteins (VSGs), isolated from some antigenic types of trypanosomes, degraded during isolation. We show that this degradation occurred immediately after breakage of the organism, presumably because of liberation of internal enzymes, and resulted in heterogeneity of isolated VSGs with respect to charge and/or molecular weight. Degradation and consequent heterogeneity of these VSGs could be abolished by releasing VSG from the trypanosome surface without breakage of the organism. The method was a modification of an incubation and shaking procedure initially described for Trypanosoma congolense (Reinwald, Rautenberg & Risse, 1979). WaTat 1.11 VSG released by this method and isolated, had a molecular weight (mol.wt) of 63000 and bound to a heterologous anti-VSG serum. VSG isolated from the same trypanosomes following breakage of organisms was of lower molecular weight. One such WaTat 1.11 VSG fragment of 42000 mol. wt, did not bind to the heterologous anti-VSG serum and therefore lacked cross-reacting antigenic determinants present in the 63000 mol. wt VSG.