Peptoid-Peptide Hybrid Analogs of the Enterococcus faecalis Fsr Auto-Inducing Peptide (AIP) Reveal Crucial Structure-Activity Relationships.

As multidrug-resistant bacteria become a more pressing risk to human health, alternate approaches to treating bacterial infections are being increasingly investigated. Enterococcus faecalis is an opportunistic pathogen responsible for a large percentage of secondary enterococci infections. Its pathogenicity has been shown to be largely dependent on a cell-density communication mechanism, termed quorum sensing. In this study, we conducted a systematic investigation of the lactone-containing macrocyclic signaling peptide used by E. faecalis for Fsr-mediated communication, termed gelatinase biosynthesis activating pheromone (GBAP). Specifically, through a combination of the on-resin sub-monomer and solution phase peptoid building block synthesis approaches, we successfully synthesized a library of peptoid-peptide hybrid analogs of GBAP and determined the biological effects associated with the introduction of the peptoid (N-alkyl glycine derivative) modifications. Within the macrocycle region of the peptide, as have been seen with other modifications, the F7 site was unusually tolerant toward peptoid modification, compared with other macrocyclic sites. Interestingly, within the exocyclic tail, peptoid modification at the N2 site completely abolished activity, a first for a single tail modification.

Development and utilization of peptide-based quorum sensing modulators in Gram-positive bacteria.

Quorum sensing (QS) is a mechanism by which bacteria regulate cell density-dependent group behaviors. Gram-positive bacteria generally rely on auto-inducing peptide (AIP)-based QS signaling to regulate their group behaviors. To develop synthetic modulators of these behaviors, the natural peptide needs to be identified and its structure-activity relationships (SARs) with its cognate receptor (either membrane-bound or cytosolic) need to be understood. SAR information allows for the rational design of peptides or peptide mimics with enhanced characteristics, which in turn can be utilized in studies to understand species-specific QS mechanisms and as lead scaffolds for the development of therapeutic candidates that target QS. In this review, we discuss recent work associated with the approaches used towards forwarding each of these steps in Gram-positive bacteria, with a focus on species that have received less attention.

Rational Design of Potent Activators and Inhibitors of the Enterococcus faecalis Fsr Quorum Sensing Circuit.

The increasing rate of resistance development to conventional antibiotics by bacteria necessitates the identification of alternative treatment possibilities that can reduce the ability of bacteria to adapt. Enterococcus faecalis remains the leading cause of clinical enterococci infections and has exhibited quorum sensing (QS)-dependent pathogenicity. Here, we report the development of macrocyclic peptide-based activators and inhibitors of the E. faecalis Fsr QS circuitry. To this end, we developed, optimized, and compared three synthetic routes for lactone-containing macrocyclic peptide scaffolds. We then utilized previous and current structure-activity relationship (SAR) insights of the native QS signaling peptide to rationally design the most potent activators and inhibitors of the Fsr QS circuitry identified to date. The application of these peptides could provide a means to attenuate the pathogenicity of E. faecalis without introducing significant selective pressure on the bacteria to develop resistance.

An Entirely Solid Phase Peptide Synthesis-Based Strategy for Synthesis of Gelatinase Biosynthesis-Activating Pheromone (GBAP) Analogue Libraries: Investigating the Structure-Activity Relationships of the Enterococcus faecalis Quorum Sensing Signal.

The development of an entirely solid-phase peptide synthesis (SPPS)-based synthesis of the quorum sensing signal gelatinase biosynthesis-activating pheromone (GBAP) from Enterococcus faecalis is reported. The method was used to prepare three libraries of analogues to investigate the structure-activity relationships (SARs) of the GBAP signal. The SAR studies revealed new characteristics of the GBAP signal and uncovered the most potent quorum sensing activator in E. faecalis known to date.