The effects and mechanisms of novel antibacterial amyloid peptides derived from Streptococcus mutans proteome

Streptococcus mutans (S. mutans) is one of the primary cariogenic pathogens. Recently the aggregation prone region (APR) has been applied to develop novel antibacterial amyloid peptides due to its ability to target and trigger the aggregation of proteins containing similar APRs. In this study, we modified 63 novel amyloid peptides based on the APRs screened from S. mutans proteome. Three of the peptides exhibited significant antibacterial activity against S. mutans, but without specificity. Transmission electron microscope (TEM), stain of Congo red and ThT, and Fourier transform infrared spectroscopy (FTIR) showed that the antimicrobial amyloid peptides (C9 and C12) aggregated into unmature fibrils, not typical morphology of mature amyloid fibrils. Distortion and perforation of cell membrane were observed by various microscopes. Membrane permeabilization assay and SYTO9/PI staining assay verified that the membrane permeability increased after being treated by C9 and C12. Aggregates and unmature fibrils could be observed inside dead cells in the ultrathin sections by TEM. Transcriptome sequencing (RNA-seq) detected the significant expression changes of genes related to protein aggregates formation (dnaK, groL and groES) and metabolism (gtfB), which was further verified by quantitative real-time PCR (qRT-PCR). In conclusion, we innovatively developed antimicrobial amyloid peptides based on the APRs in S. mutans proteome and found their combination antimicrobial mechanism of damaging the membrane with triggering protein aggregation, which might shed light on novel antibacterial peptides development.