Killing of Trypanosoma brucei by concanavalin A: Structural basis of resistance in glycosylation mutants

Concanavalin A (Con A) kills procyclic (insect) forms of Trypanosoma brucei by binding to N-glycans on EP-procyclin, a major surface glycosyl phosphat idylinositol (GPI)-anchored protein which is rich in Glu-Pro repeats. We ha ve previously isolated and studied two procyclic mutants (ConA 1-1 and ConA 4-1) that are more resistant than wild-type (WT) to Con A killing. Althoug h both mutants express the same altered oligosaccharides compared to WT cel ls, ConA 4-1 is considerably more resistant to lectin killing than is ConA 1-1. Thus, we looked for other alterations to account for the differences i n sensitivity. Using mass spectrometry, together with chemical and enzymati c treatments, we found that both mutants express types of EP-procyclin that are either poorly expressed or not found at all in WT cells. ConA 1-1 expr esses mainly EP1-3, a novel procyclin that contains 18 EP repeats, is parti ally N-glycosylated, and bears hybrid-type glycans. On the other hand, ConA 4-1 cells express almost exclusively EP2-3, a navel non-glycosylated procy clin isoform with 23 EP repeats and no site for glycosylation. The predomin ance of EP2-3 in ConA 4-1 cells explains their high resistance to ConA kill ing. Thus, switching the procyclin repertoire, a process that could be rele vant to parasite development in the insect vector, modulates the sensitivit y of trypanosomes to cytotoxic lectins. (C) 2000 Academic Press.