Molecular analysis of Phr peptide processing in Bacillus subtilis

Area of Science:

• Microbiology
• Molecular Biology
• Cellular Biology

Background:

• Bacillus subtilis utilizes an export-import pathway for Phr pentapeptide inhibitors, crucial for Rap protein regulation.
• These inhibitors, including PhrA, PhrE, and PhrC, target specific phosphatases (RapA, RapE, RapC) involved in initiating sporulation and competence development.
• Rap phosphatases act on Spo0F~P and ComA response regulators, key components of the phosphorelay and competence pathways.

Purpose of the Study:

• To investigate the processing mechanism of Phr preinhibitor proteins into active pentapeptide inhibitors in Bacillus subtilis.
• To determine the role of type I signal peptidases (SipS, SipT, SipU, SipV, SipW) in Phr processing.
• To elucidate the function of specific signal peptidases in bacterial development.

Main Methods:

• In vivo and in vitro analyses were employed to study Phr processing.
• Mutational analysis of Bacillus subtilis signal peptidase genes (sipS, sipT, sipU, sipV, sipW).
• Phenotypic analysis of mutant strains concerning sporulation, competence, and cell growth.

Main Results:

• Phr preinhibitor proteins undergo a single processing event at the N-terminal end of the pentapeptide.
• This processing is independent of type I signal peptidase activity; none of the five signal peptidases are essential for Phr processing.
• SipV and SipT were found to have previously undescribed roles in Bacillus subtilis sporulation, competence, and cell growth.

Conclusions:

• The processing of Phr preinhibitors into active pentapeptide inhibitors in Bacillus subtilis is not mediated by type I signal peptidases.
• Signal peptidases SipV and SipT possess novel functions essential for bacterial development and growth.
• Understanding Phr processing and signal peptidase roles provides insights into the regulation of sporulation and competence.