| Abstract: | The Saccharomyces cerevisiae secretory process was studied by evaluating secretion efficiency, processing efficiency, and the efficiency of protein folding for hybrid proteins containing the yeast prepro-alpha-factor leader region. Secretion of three proteins, beta-endorphin, calcitonin, and a consensus alpha-interferon (IFN-Con1), were compared in terms of secretion efficiency into the culture medium, beta-Endorphin and calcitonin, both small proteins, were found to be efficiently secreted from logarithmically grown cells. In contrast, the larger IFN-Con1 accumulated in the periplasmic space and cell wall. The glycosylated, unprocessed prepro-alpha-factor/IFN-Con1 fusion protein was also found to be secreted into the culture medium. The presence of (Glu-Ala) dipeptides in the alpha-factor spacer peptide increased the efficiency of cleavage at Lys-Arg in the prepro-alpha-factor/IFN-Con1 protein fusion. Purified secreted IFN-Con1 was structurally characterized to determine the effect of passage through the yeast secretory pathway on the fidelity and efficiency of protein folding. The disulfide structure of the secreted protein was found to be identical with that reported for the native human alpha-interferons. |
