The 19-residue pro-peptide of staphylococcal nuclease has a profound secretion-enhancing ability in Escherichia coli

Staphylococcus aureus secretes two forms of extracellular nuclease, nuclease A and nuclease B. Nuclease A, consisting of 149 residues, is a proteolytic product of nuclease B, which is a processing intermediate that has a 19-residue N-terminal pro-peptide between the signal peptide and nuclease A. It has been shown that nuclease A can be secreted by Escherichia coli by fusing it to the OmpA signal peptide. We now demonstrate that the addition of the pro-peptide between the OmpA signal peptide and nuclease A leads to a significantly enhanced secretion rate in E. coli. The processing and secretion rates of nuclease B at 37 degrees C were at least 10 times faster than those of nuclease A. Nuclease B was also secreted efficiently under conditions which blocked the secretion of nuclease A, such as secA mutations and the addition of phenethyl alcohol or sodium azide. This enhancing effect of the pro-peptide was not as striking when it was attached to beta-lactamase, indicating that the pro-peptide acts as a specific secretion enhancer for nuclease A. Equilibrium circular dichroism on purified nuclease A and nuclease B indicated that the pro-peptide itself had no significant destabilizing effect on the mature protein. The existence of similar pro-peptides in Gram-positive bacterial secretory proteins indicates that they may also serve as secretion enhancers for individual proteins.