Expression of cholera toxin B subunit in Saccharomyces cerevisiae

Cholera toxin, secreted by Vibrio cholerae, consists of A and B subunits. Cholera toxin B subunit (CTB) is used in many sci- entific researches. It has already been expressed in several bacterial and plant systems. In order to express CTB protein in Saccha- romyces cerevisiae, the expression plasmid pCTB83 was constructed by inserting ctxB gene in pYES2 shuttle vector. The new construct was transferred into S. cerevisiae cells and the ctxB gene was induced with 2% galactose. SDS-PAGE analysis showed the presence of CTB in yeast lysate and immunoblotting analysis of yeast total soluble protein indicated that the yeast-derived CTB protein was anti- genically indistinguishable from bacterial CTB protein. Quantitative ELISA showed that the maximum amount of CTB protein expressed in yeast was approximately 1.8% of total soluble protein. CTB is a subunit vaccine candidate against cholera. Since the whole recom- binant yeast has been introduced as a new vaccine formulation, expression of ctxB in S. cerevisiae may offer an effective and inex- pensive strategy to protect people against cholera in high-risk areas.