A Membrane-Targeted Peptide Inhibiting PtxA of Phosphotransferase System Blocks <b><i>Streptococcus mutans</i></b>

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.