Pharmacological Evaluation of Synthetic Dominant-Negative Peptides Derived from the Competence-Stimulating Peptide of Streptococcus pneumoniae

Designing Highly Potent Side-Chain Lactam-Bridged Cyclic Competence-Stimulating Peptide-Based Quorum-Sensing Modulators in Streptococcus oligofermentans

Streptococcus oligofermentans, a Gram-positive bacterium found in the oral microbiome, shows promise as an oral probiotic for preventing dental caries. It exhibits a reverse correlation with Streptococcus mutans, a key caries-causing pathogen, likely due to its production of hydrogen peroxide, a process mediated by quorum sensing (QS). In this work, we set out to develop novel lactam-based cyclic analogues of the competence stimulating peptide (CSP) signal utilized by S. oligofermentans for QS activation. To this end, we first conducted a ring position scan, where we determined the best positions within the CSP sequence to use for macrolactamization. We then conducted systematic ring size and bridge position scans to fine-tune the cyclic peptide conformation and identified a cyclic analogue, CSP-cyc(K2E2), with enhanced biological activity, 7-fold more active than the native CSP signal. This analogue also exhibited improved stability toward enzymatic degradation, demonstrating this analogue's potential utility as a chemical probe to study interspecies interactions between oral microbes and as a potential therapeutic agent. Overall, our lead cyclic analogue could be applied to augment the biotherapeutic potential of S. oligofermentans against S. mutans infections.

Designing and synthesizing peptide-based quorum sensing modulators

Quorum sensing (QS) is a density-dependent bacterial communication system that uses small molecules as regulatory modulators. Synthetic changes to these molecules can up-or-down-regulate this system, leading to control of phenotypes, like competence and virulence factor production, that have implications in human health. In this chapter, a methodology for library design and screening of synthetic autoinducing peptides (AIPs) to uncover QS SARs is delineated. Additionally, procedures for the synthesis, purification and analysis of linear and cyclic AIPs are detailed. This includes solutions for potential synthetic challenges including diketopiperazine formation when using N-methyl amino acids and cyclization of peptides containing N-terminal cysteine residues. These procedures have and are currently being applied to develop potent QS modulators in Streptococcus pneumoniae, Bacillus cereus, Streptococcus gordonii and Lactiplantibacillus plantarum.

Targeting Peptide-Based Quorum Sensing Systems for the Treatment of Gram-Positive Bacterial Infections

Bacteria utilize a cell density-dependent communication system called quorum sensing (QS) to coordinate group behaviors. In Gram-positive bacteria, QS involves the production of and response to auto-inducing peptide (AIP) signaling molecules to modulate group phenotypes, including pathogenicity. As such, this bacterial communication system has been identified as a potential therapeutic target against bacterial infections. More specifically, developing synthetic modulators derived from the native peptide signal paves a new way to selectively block the pathogenic behaviors associated with this signaling system. Moreover, rational design and development of potent synthetic peptide modulators allows in depth understanding of the molecular mechanisms that drive QS circuits in diverse bacterial species. Overall, studies aimed at understanding the role of QS in microbial social behavior could result in the accumulation of significant knowledge of microbial interactions, and consequently lead to the development of alternative therapeutic agents to treat bacterial infectivity. In this review, we discuss recent advances in the development of peptide-based modulators to target QS systems in Gram-positive pathogens, with a focus on evaluating the therapeutic potential associated with these bacterial signaling pathways.