Effect of EPS1 gene deletion in Saccharomyces cerevisiae on the secretion of foreign proteins which have disulfide bridges

Both amyloid-prone cystatin and unstable mutant C94A lysozyme were secreted in wild-type and Δeps1 Saccharomyces cerevisiae cells. Amyloid-prone cystatin secreted at much higher level in Δeps1 cells than that in wild-type yeast. In parallel, the secretion amount of disulfide bond disrupted mutant C94A lysozyme greatly increased in Δeps1 cells although that was apparently low in wild-type yeast cells compared with the secretion amount of wild-type lysozyme. It is interesting that neither the unstable mutant C94A lysozyme nor amyloid-prone cystatin secreted in Δeps1 cells maintained their specific activities. These observations lead to the supposition that yeast cells deficient for the protein disulfide isomerase-family-member EPS1 locus secrete more of labile disulfide-containing model proteins.