A multicomponent protein complex mediates environmental stress signaling in Bacillus subtilis

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The activity of the sigma(B) transcription factor in Bacillus subtilis is regulated by a partner-switching mechanism involving serine phosphorylation.
• Stress signals are transmitted to sigma(B) through independent pathways, each involving a serine phosphatase that controls partner-switching regulators.

Purpose of the Study:

• To investigate the regulation of the RsbU environmental signaling phosphatase.
• To test the existing model where RsbS is the sole negative regulator of RsbU.
• To identify additional components involved in environmental stress signaling to sigma(B).

Main Methods:

• Genetic analysis to test protein function in vivo.
• Biochemical assays to study protein interactions and complex formation.
• Protein purification using nickel affinity and gel-filtration chromatography.

Main Results:

• The model stating RsbS is the sole negative regulator of RsbU was invalidated.
• A family of four co-antagonist proteins (RsbRA-D) were identified, each with domains similar to RsbS.
• Any single RsbR protein, along with RsbS, was sufficient to enable environmental signaling, indicating redundant co-antagonist function.
• A multicomponent complex containing RsbRA, RsbRB, and RsbS was purified, suggesting a functional signaling unit.

Conclusions:

• RsbS alone is insufficient for negative regulation of RsbU; RsbR proteins are required as redundant co-antagonists.
• The identified multicomponent complex likely acts as a signaling machine for transmitting environmental stress signals to sigma(B).
• The properties of this complex may play a role in the precise sensing of environmental stress.