ABSTRACT
Simultaneous expression of the Fd (truncated heavy chain) and light chain gene in Saccharomyces cerevisiae resulted in secretion of a properly folded and assembled Fab fragment that bound to target cancer cells. Differently from expression in the cytoplasm, a strong promoter or culturing the host cell at 37 C is not always effective for expression, probably because the secretion is coupled with translation of the protein. The amount of functional Fab fragment in the periplasmic space as well as and culture medium were measured by enzyme-linked immunosorbent assay. Functional Fab could be found in both the periplasm and the culture medium. The Fab in the medium probably leaked from the periplasm, since the periplasmic Fab level gradually decreased with longer incubation times. The presence of the protein agregates enabled us to purify the Fd fragment and light chain easily, along with E. coli insoluble proteins.
