Optimization of the signal-sequence cleavage site for secretion from Bacillus subtilis of a 34-amino acid fragment of human parathyroid hormone.

We have effected the secretion from Bacillus subtilis of a 34-amino acid (aa) fragment of human parathyroid hormone (PTH,1-34), using a Bacillus amyloliquefaciens neutral protease signal sequence. The secretion efficiency depended on the aa sequence near the signal-sequence cleavage site. We constructed a series of gene fusions encoding different pairs of aa between the signal sequence and PTH,1-34. There was a correlation between those polypeptides which were efficiently secreted and the potential for a beta-turn in the region just beyond the signal-sequence cleavage site. Based on this correlation, we constructed a gene fusion which specified Gly rather than Ala at the C terminus of the signal sequence, thus creating a beta-turn potential at the end of the signal sequence. The change provided a slight increase in secretion efficiency.