Secretion of human epidermal growth factor from Saccharomyces cerevisiae using synthetic leader sequences

We have investigated different leader sequences for their ability to direct the efficient secretion of human epidermal growth factor (hEGF) from Saccharomyces cerevisiae. We designed a consensus signal sequence which directs secretion of hEGF from yeast as efficiently as the yeast invertase signal sequence. However, secretion is increased over fivefold by the introduction, after the signal sequence, of a synthetic 19-amino acid (aa) pro-sequence containing a cleavage recognition site for the KEX2 protease. Even in the absence of an Asn-linked glycosylation site, secretion of hEGF using the synthetic prepro-leader was as efficient as that directed by the alpha-factor leader. The role of the KEX2 protease cleavage site was investigated by mutation of the yeast alpha-factor KEX2 site (cleavage after Lys-Arg). Cleavage was obtained with the following order of efficiency, Lys-Arg greater than Pro-Arg greater than Asp-Arg, although the sequence context was also found to affect efficiency.