Molecular characterization of two invariant surface glycoproteins specific for the bloodstream stage of Trypanosoma brucei.

In the accompanying paper (Ziegelbauer, K., and Overath, P. (1992) J. Biol. Chem. 267, 10791-10796), two invariant surface glycoproteins, ISG65 and ISG75, were identified in the mammalian stage of the parasitic protozoan, Trypanosoma brucei. In this study, the genes coding for these proteins have been isolated. Their nucleotide sequence suggests no relationship to other known genes and predicts polypeptides with NH2-terminal signal sequences, hydrophilic extracellular domains, single trans-membrane alpha-helices, and short cytoplasmic domains. ISG65 and ISG75 are expressed in bloodstream forms (70,000 and 50,000 molecules/cell, respectively) but not in the insect midgut stage. They can be detected in all T. brucei brucei variant clones investigated. Both polypeptides are distributed over the entire surface of the parasite.