Gene Regulation by the LiaSR Two-Component System in Streptococcus mutans

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• The LiaSR two-component system is crucial for bacterial stress tolerance, including responses to cell envelope damage, acid, antibiotics, and detergents.
• In Streptococcus mutans, a dental pathogen, LiaSR is essential for surviving oral cavity stresses.

Purpose of the Study:

• To elucidate the molecular mechanisms of LiaSR-mediated gene regulation in S. mutans.
• To identify novel target genes and DNA binding motifs of the LiaR response regulator.

Main Methods:

• Site-directed mutagenesis of the conserved phosphorylation site in LiaR (D58A).
• Electrophoretic mobility shift assays (EMSAs) to assess LiaR binding to promoter regions.
• Bioinformatic analysis to identify conserved DNA motifs and genome-wide scanning for motif occurrence.

Main Results:

• The D58A LiaR mutant was deficient in DNA binding.
• LiaR did not bind the lia operon promoter but bound promoters of SMU.753, SMU.2084, and SMU.1727.
• A novel 25-bp conserved motif essential for LiaR binding was identified and validated.
• The hrcA gene promoter contains the LiaR binding motif, and hrcA is negatively regulated by LiaSR.

Conclusions:

• The LiaSR system in S. mutans utilizes a newly defined DNA motif for target gene regulation.
• LiaSR plays a role in regulating the heat shock response through negative control of hrcA.