From Antibacterial Activity to Molecular Mechanism: Case Study of Hexapeptide RWWRWW and Its Analogues.

In recent years, antimicrobial peptides (AMPs) have emerged as a potent weapon against the growing threat of antibiotic resistance. Among AMPs, the ones containing tryptophan (W) and arginine (R) exhibit enhanced antimicrobial properties, benefiting from the unique physicochemical features of the two amino acids. Herein, we designed three hexapeptides, including WR, DWR (_D-isomer), and RF, derived from the original sequence, RWWRWW-NH₂ (RW). By combining sum frequency generation vibrational spectroscopy (SFG-VS) and molecular dynamics (MD) simulation, we examined AMPs' interactions with model bacterial membrane at the molecular level. Our findings revealed the innate different structural features associated with molecular aggregation and membrane activity between _L-(WR, RF and RW) and _D-isomer. The _D-isomer was demonstrated to aggregate via intermolecular hydrogen bonding, which reduced its membrane adsorption quantity and consequently weakened its disruptive effect on the model membrane; while _L-isomers rarely aggregated and thus could fully interact with the model membrane. _D-isomer was proven to lack a stable helical structure, while _L-isomers adopted helical structures, which was believed to be the reason for DWR's tendency to aggregate easily. This study should contribute to designing novel short-chain AMPs with high efficiency, especially in the case that _D-isomers will be used.