Type I signal peptidases of Bacillus subtilis

Bacillus subtilis contains at least three chromosomally-encoded type I signal peptidases (SPases; SipS, SipT, and SipU), which remove signal peptides from secretory proteins. In addition, certain B. subtilis (natto) strains contain plasmid-encoded type I SPases (SipP). The known type I SPases from B. subtilis show a high degree of similarity to SPases from related bacilli and Staphylococcus aureus and, to a lesser extent, to SPases from other organisms. In addition, the putative active site region of the Bacillus SPases shows similarity to the corresponding region of LexA-like proteases, suggesting that the type I SPases employ a serine-lysine catalytic dyed. Unlike the type I SPase of Escherichia coli, Sips, SipT and SipU are neither essential for protein secretion, nor for viability of the cell. Although non-essential, Sips is an important factor for efficient protein secretion. SipS is transcribed in a growth phase-and medium-dependent manner. Under some conditions, transcription of sipS is controlled by the DegS-DegU two-component regulatory system, indicating that expression of sipS is determined by the same factors that control the expression of most genes for secreted degradative enzymes. These observations suggest thats. subtilis can modulate its capacity and specificity for protein secretion through controlled expression of sipS.