Expression of Trypanosoma brucei procyclin as a fusion protein in Escherichia coli.

Procyclin, a glycoprotein surface antigen of procyclic forms of Trypanosoma brucei, was expressed in Escherichia coli as a cro-beta-galactosidase fusion protein. Antibodies produced in rabbits immunised with gel-purified fusion protein bound to the surface of living procyclic culture forms in indirect immunofluorescence assays and were able to immunoprecipitate procyclin from lysates of trypanosomes biosynthetically labelled with tritiated proline. In addition, the antibodies recognised synthetic peptides corresponding to three different regions of the procyclin molecule, including a glutamic acid-proline dipeptide repeat. The results indicate that T. brucei procyclin expressed as a fusion protein is immunogenic and antigenically intact. In contrast, no rabbit antibodies could be produced against a 16-amino-acid synthetic peptide consisting of the dipeptide repeat, even when the peptide was coupled to carrier proteins.