A Membrane-Targeted Peptide Inhibiting PtxA of Phosphotransferase System Blocks Streptococcus mutans

Abstract

Streptococcus mutans, the primary cause of dental caries, takes up carbohydrates through the phosphoenolpyruvate sugar phosphotransferase system (PTS). This study aimed to identify a novel membrane-targeted antimicrobial peptide (AMP) that could also target the L-ascorbate-specific PtxA component of the S. mutans PTS system. C10-KKWW was identified and selected using virtual screening of a lipopeptide library, a minimum inhibiting concentration (MIC) assay, cytotoxicity assays and a hemolysis assay. Surface plasmon resonance confirmed that C10-KKWW had a high binding affinity for PtxA. Combining with scanning electron microscopy and cell permeability assay, it was shown that the effects of C10-KKWW could be attributed to both membrane and PtxA. Wild type (WT) S. mutans, a ptxA deletion mutant (ΔptxA), and a mutant-complemented strain (CptxA), were cultured consistently in brain heart infusion (BHI) medium, tryptone-vitamin medium supplemented with 15 mM L-ascorbate (TVL), or for 5 h in BHI supplemented with 7.4 mM sodium L-ascorbate. Compared to ∆ptxA, in WT S. mutans and CptxA, C10-KKWW had a stronger MIC (3.9 μg/mL), and distinctively decreased biofilm viability. The extracellular concentrations of L-ascorbate/sodium L-ascorbate were not changed before and after WT treated with C10-KKWW. L-ascorbate-induced operon genes, or other PTS genes, were significantly suppressed by C10-KKWW. In conclusion, C10-KKWW has been developed; it acts through interaction with the bacterial membrane and interferes with L-ascorbate translocation to inhibit S. mutans growth and eradicate its biofilm. C10-KKWW may be especially effective at optimal oral ascorbate levels. A combination of C10-KKWW with sodium L-ascorbate might also be a novel strategy for dental caries treatment.