Structure-function analysis for the development of peptide inhibitors for a Gram-positive quorum sensing system

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The Streptococcus pneumoniae Rgg144/SHP144 regulator-peptide quorum sensing (QS) system is essential for nutrient utilization, oxidative stress response, and virulence.
• Quorum sensing systems regulate bacterial behavior based on population density.

Purpose of the Study:

• To characterize the Streptococcus pneumoniae Rgg144/SHP144 quorum sensing system.
• To identify key residues within the short hydrophobic peptide (SHP) essential for receptor activation and function.

Main Methods:

• Alanine-scanning mutagenesis of the SHP144 peptide.
• Assessment of receptor binding affinity and transcriptional activation of mutant peptides.
• Pangenome comparison of SHP144 allelic variants.
• Crystallization of the Rgg144 receptor.

Main Results:

• Mutations in SHP144 differentially affected receptor binding and transcriptional activation.
• A proline substitution at residue 21 (P21A) significantly reduced transcriptional activation (29-fold) while increasing binding affinity (3-fold).
• The P21A mutation resulted in decreased mannose utilization and increased susceptibility to paraquat, consistent with Rgg144 function.
• P21 is fully conserved across SHP144 allelic variants.

Conclusions:

• Key interactions within the SHP144 peptide are critical for Rgg144-mediated transcriptional activation.
• Targeting specific residues like P21 offers potential for developing broad-spectrum QS inhibitors.
• The study provides insights into the mechanism of Rgg144 activation and its potential as a therapeutic target.