Harnessing Multiple, Nonproteogenic Substitutions to Optimize CSP:ComD Hydrophobic Interactions in Group†1 Streptococcus pneumoniae.

Streptococcus pneumoniae (pneumococcus) is a human pathobiont that causes drastic antibiotic-resistant infections and is responsible for millions of deaths universally. Pneumococcus pathogenicity relies on the competence-stimulating peptide (CSP)-mediated quorum-sensing (QS) pathway that controls competence development for genetic transformation and, consequently, the spread of antibiotic resistance and virulence genes. Modulation of QS in S. pneumoniae can therefore be used to enervate pneumococcal infectivity as well as minimize the susceptibility to resistance development. In this work, we sought to optimize the interaction of CSP1 with its cognate transmembrane histidine kinase receptor (ComD1) through substitution of proteogenic and nonproteogenic amino acids on the hydrophobic binding face of CSP1. The findings from this study not only provided additional structure-activity data that are significant in optimizing CSP1 potency, but also led to the development of potent QS modulators. These CSP-based QS modulators could be used as privileged scaffolds for the development of antimicrobial agents against pneumococcal infections.

The importance of the PapR7 C-terminus and amide protons in mediating quorum sensing in Bacilluscereus.

The opportunistic human pathogen Bacillus cereus controls the expression of key infection-promoting phenotypes using bacterial quorum sensing (QS). QS signal transduction within the species is controlled by an autoinducing peptide, PapR7, and its cognate receptor, PlcR, indicating that the PlcR:PapR interface is a prime target for QS inhibitor development. The C-terminal region of the peptide (PapR7; ADLPFEF) has been successfully employed as a scaffold to develop potent QS modulators. Despite the noted importance of the C-terminal carboxylate and amide protons in crystallographic data, their role in QS activity has yet to be explored. In this study, an N-methyl scan of PapR7 was conducted in conjunction with a C-terminal modification of previously identified B. cereus QS inhibitors. The results indicate that the amide proton at Glu6 and the C-terminal carboxylate are important for effective QS inhibition of the PlcR regulon. Through ß-galactosidase and hemolysis assays, a series of QS inhibitors were discovered, including several capable of inhibiting QS with nanomolar potency. These inhibitors, along with the structure-activity data reported, will serve as valuable tools for disrupting the B. cereus QS pathway towards developing novel anti-infective strategies.

Optimizing CSP1 analogs for modulating quorum sensing in Streptococcus pneumoniae with bulky, hydrophobic nonproteogenic amino acid substitutions.

The prompt appearance of multiantibiotic-resistant bacteria necessitates finding alternative treatments that can attenuate bacterial infections while minimizing the rate of antibiotic resistance development. Streptococcus pneumoniae, a notorious human pathogen, is responsible for severe antibiotic-resistant infections. Its pathogenicity is influenced by a cell-density communication system, termed quorum sensing (QS). As a result, controlling QS through the development of peptide-based QS modulators may serve to attenuate pneumococcal infections. Herein, we set out to evaluate the impact of the introduction of bulkier, nonproteogenic side-chain residues on the hydrophobic binding face of CSP1 to optimize receptor-binding interactions in both of the S. pneumoniae specificity groups. Our results indicate that these substitutions optimize the peptide-protein binding interactions, yielding several pneumococcal QS modulators with high potency. Moreover, pharmacological evaluation of lead analogs revealed that the incorporation of nonproteogenic amino acids increased the peptides' half-life towards enzymatic degradation while remaining nontoxic. Overall, our data convey key considerations for SAR using nonproteogenic amino acids, which provide analogs with better pharmacological properties.