Design of β-hairpin pepticles with potent antimicrobial activity and target specificity against Enterococcus faecalis

摘要

Most classical antibiotics have broad spectra of activity, killing benign and pathogenic organisms indiscriminately. The ecological disruption resulting from antibiotic treatment frequently results in secondary infections or other negative clinical consequences. The problems resulting from wide-spectrum antibiotic use, combined with the emergence of drug-resistant strains, highlight the fundamental need for new "targeted" antibiotic therapies to combat pathogens with a minimal impact on normal microflora. Antimicrobial pepticles (AMPs), which exert their activities by physical disruption of microbial cell membranes are amongst the most promising candidates for the development of novel antibacterial materials. Recently, we developed a new class of linear tryptophan zipper (trpzip)-like β-hairpin AMPs, which possess antimicrobial activities against both gram-positive and gram-negative bacteria. In the present study, a series of Enterococcus faecalis-targeted AMPs were constructed as a model for targeted antibiotics against specific bacteria. To target the broad-spectrum AMPs to the cell membranes of E. faecalis, the enterococcal peptide pheromone cCF10 was linked to the N-terminus or the C-terminus of trpzip pepticles, respectively. This pheromone cCF10 is a species-specific signaling molecule could traverse the cell wall and bind to its receptor with a high affinity. The results showed that the hybrid pepticles containing enterococcal pheromone at the N terminus exhibit greatly enhanced antimicrobial activities and selectivity against E. faecalis when compared to the parental pepticles. The specificity of pheromonicin was shown by a dose-dependent inhibition of the antimicrobial effects of hybrid pepticles by competition with free cCF10 pheromone. Similarly, a construct in which a random peptide of the same length as cCF10 fused to the N terminus of trpzip pepticles did not exhibit any inhibitory effects to targeted bacteria. These results indicate that the specifically antimicrobial activities of the designed pepticles against E. faecalis are receptor dependent. Electron microscopy and fluorescence spectroscopy studies indicated that pheromone-guided hybrid pepticles exert their activities by permeabilizing the microbial membrane and damaging cell membrane integrity. This study provides new insights into the design of targeted antimicrobial pepticles which could selectively eliminate pathogens while preserving the protective benefits of a healthy normal flora.