Translational fusion of heat labile enterotoxin chain B and beta-subunit of human chorionic gonadotropin: periplasmic expression in Escherichia coli and its immunogenicity.

A fusion gene was constructed consisting of heat labile enterotoxin chain B (LTB) of E. coli genetically linked at its C-terminus to the beta-subunit of human chorionic gonadotropin in translational fusion, under the control of tac promoter and LTB signal sequence. Expression of the fusion gene (about 5 microgram/ml) in E. coli was confirmed by immunoblot analysis using both anti-LTB and anti-betahCG polyclonal antibodies. The fusion protein was efficiently processed and exported to the periplasmic space. LTB in the fusion protein retained its ability to bind to GM1 ganglioside receptor. Mice immunized with the fusion protein produce antibodies that recognize recombinant betahCG and the native hCG suggesting its potential use as a contraceptive vaccine.