Pheromone Recognition and Selectivity by ComR Proteins among Streptococcus Species

Area of Science:

• Microbiology
• Bacterial genetics
• Molecular biology

Background:

• Natural transformation enables bacteria to acquire new traits, including antibiotic resistance.
• In Streptococcus, competence is regulated by quorum sensing (QS) via the ComRS system, involving ComS peptides and the ComR transcription factor.
• Divergence in ComS/XIP and ComR sequences suggests species-specific communication.

Purpose of the Study:

• Investigate inter-species cross-talk in Streptococcus competence regulation.
• Elucidate the molecular interaction between ComR and XIP peptides.
• Determine structural basis for XIP recognition and specificity.

Main Methods:

• Developed an in vivo 'test-bed' assay to assess ComR activity with various XIP peptides.
• Determined the X-ray crystal structure of Streptococcus suis ComR.
• Utilized site-directed mutagenesis to probe the XIP-binding pocket in vitro and in vivo.

Main Results:

• Identified distinct ComR specificity classes: strict, intermediate, and promiscuous.
• Revealed structural features of the ComR XIP-binding pocket, with conserved and variable faces.
• The conserved face mediates ligand binding, while the variable face dictates XIP peptide specificity.

Conclusions:

• Established a model for XIP recognition and specificity in Streptococcus.
• The findings explain species-specific communication and enable prediction of novel XIP peptides.
• Provides insights into the evolution of bacterial competence and horizontal gene transfer.