The antimicrobial lysine-peptoid hybrid LP5 inhibits DNA replication and induces the SOS response in Staphylococcus aureus

Abstract

BackgroundThe increase in antibiotic resistant bacteria has led to renewed interest in development of alternative antimicrobial compounds such as antimicrobial peptides (AMPs), either naturally-occurring or synthetically-derived. Knowledge of the mode of action (MOA) of synthetic compounds mimicking the function of AMPs is highly valuable both when developing new types of antimicrobials and when predicting resistance development. Despite many functional studies of AMPs, only a few of the synthetic peptides have been studied in detail.ResultsWe investigated the MOA of the lysine-peptoid hybrid, LP5, which previously has been shown to display antimicrobial activity against Staphylococcus aureus. At concentrations of LP5 above the minimal inhibitory concentration (MIC), the peptoid caused ATP leakage from bacterial cells. However, at concentrations close to the MIC, LP5 inhibited the growth of S. aureus without ATP leakage. Instead, LP5 bound DNA and inhibited macromolecular synthesis. The binding to DNA also led to inhibition of DNA gyrase and topoisomerase IV and caused induction of the SOS response.ConclusionsOur data demonstrate that LP5 may have a dual mode of action against S. aureus. At MIC concentrations, LP5 binds DNA and inhibits macromolecular synthesis and growth, whereas at concentrations above the MIC, LP5 targets the bacterial membrane leading to disruption of the membrane. These results add new information about the MOA of a new synthetic AMP and aid in the future design of synthetic peptides with increased therapeutic potential.

Amphibian antimicrobial peptide fallaxin analogue FL9 affects virulence gene expression and DNA replication in Staphylococcus aureus

“…A dual mode of action was suggested previously for other synthetic peptides that were found to target the cell membrane when applied at high concentrations, and to have intracellular targets when used at low concentration (Patrzykat et al, 2002;Sahl et al, 2005;Gottschalk et al, 2013). Therefore, we investigated the possibility of FL9 having intracellular targets by assessing the synthesis of DNA molecules in S. aureus.…”

“…Some AMPs that inhibit DNA synthesis bind nonspecifically to DNA. For example, the amphibian AMP, the a-helical AMP buforin II, can penetrate the cell membrane without causing its disruption, and inhibits cellular functions by binding to nucleic acids (Park et al, 1998;Kobayashi et al, 2000;Rotem et al, 2008;Sarig et al, 2011;Gottschalk et al, 2013). Therefore, to investigate whether the inhibition of DNA synthesis could be due to the binding of FL9 to bacterial DNA, a gel retardation assay was performed.…”

SOS Response and Staphylococcus aureus: Implications for Drug Development

“…The compound to be tested should be added in wells in these agar plates and the expression of recA is monitored as a blue ring at the point of bacterial growth. Using this assay, the ability of some compound to active SOS response was revealed, such as the lysinepeptoid hybrid LP5 [49], some cyclic peptide inhibitors of the β-sliding clamp [50], and the amphibian peptide fallaxin analogue FL9 [51]. The induction of SOS response was also related to the anti-S. aureus action of new synthetic bis-indole antibiotics [52].…”

“…Given the role of SOS response in S. aureus survival and pathogenesis, the efects of new antimicrobial candidates on SOS genes have become more frequently evaluated, especially those which target DNA structure or DNA replication machinery [49,50]. Gotschalk et al [49] reported an easy and inexpensive agar-based assay to detect the expression of recA induced by a compound.…”

“…Gotschalk et al [49] reported an easy and inexpensive agar-based assay to detect the expression of recA induced by a compound. In this assay, a S. aureus 8325-4 derivative strain carrying the recA gene fused with the reporter gene lacZ (which encodes for β-galactosidase) is incorporated in agar plates containing X-Gal (5-bromo-4-β chloro-3-indolyl-D-galactopyranoside).…”