MglA/SspA complex interactions are modulated by inorganic polyphosphate.

Area of Science:

• Microbiology and Molecular Biology
• Bacterial Pathogenesis
• Gene Regulation

Background:

• Francisella tularensis virulence relies on Francisella pathogenicity island (FPI) genes.
• MglA and SspA transcription factors form a heterodimer complex essential for FPI gene regulation.
• The role of intracellular metabolites in modulating MglA-SspA protein interactions was unknown.

Purpose of the Study:

• To investigate if intracellular metabolites modulate the MglA-SspA protein/protein interactions.
• To identify the specific metabolite responsible for promoting MglA-SspA complex formation and function.

Main Methods:

• Yeast two-hybrid system in a polyphosphate-deficient Escherichia coli strain.
• Chromatin immunoprecipitation (ChIP) studies in F. tularensis.
• Isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC) to assess binding affinity and stability.

Main Results:

• Inorganic polyphosphate (polyP) was identified as a signal molecule promoting MglA-SspA interaction.
• PolyP stabilizes the MglA/SspA complex and its interaction with the FevR regulator.
• PolyP directly binds to the MglA/SspA complex with high affinity (KD = 0.3 µM), increasing its thermal stability.

Conclusions:

• Inorganic polyphosphate is a key regulator of MglA-SspA complex formation and function in Francisella tularensis.
• PolyP enhances the binding of the MglA/SspA complex to target gene promoters, impacting virulence.
• This discovery provides a novel target for understanding and potentially controlling F. tularensis infections.