Ligand binding represses bacterial histidine kinase activity by inhibiting its dimerization

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Two-component systems (TCS) are crucial for bacterial signal transduction.
• Sensor kinases (SKs) are key components, but their multi-ligand sensing mechanisms remain unclear.
• The *Mycobacterium tuberculosis* PdtaS/PdtaR system regulates virulence in response to copper and nitric oxide.

Purpose of the Study:

• To elucidate the mechanism by which the PdtaS sensor kinase senses chemically diverse ligands.
• To investigate how PdtaS integrates signals from copper and nitric oxide.
• To understand the structural basis for multi-ligand sensing in bacterial TCS.

Main Methods:

• In vitro biochemical assays to study PdtaS kinase activity and dimerization.
• Phylogenetic analysis of the PdtaS protein family.
• Site-directed mutagenesis of the PdtaS GAF/PAS dimer interface.
• In vivo studies in *Mycobacterium tuberculosis* cells.

Main Results:

• PdtaS is a constitutively active dimeric kinase that autophosphorylates in trans.
• Copper and nitric oxide inhibit PdtaS phosphorylation by disrupting its dimerization.
• Mutations in the conserved GAF dimer interface impair multi-ligand sensing.
• The conserved dimer interface, not ligand-binding pockets, is critical for sensing diverse inputs.

Conclusions:

• PdtaS senses diverse environmental ligands, including copper and nitric oxide, through the inhibition of dimerization-dependent phosphorylation.
• The conserved dimerization interface is a key structural element for multi-ligand sensing in this bacterial kinase.
• This mechanism provides a novel understanding of how single sensor kinases can respond to multiple environmental signals.