The continued emergence of new antibiotic resistant bacterial strains has resulted in great\ninterest in the development of new antimicrobial treatments. Antimicrobial peptides (AMPs) are\none of many potential classes of molecules to help meet this emerging need. AMPs are naturally\nderived sequences, which act as part of the innate immune system of organisms ranging from insects\nthrough humans. We investigated the antimicrobial peptide AP3, which is originally isolated from\nthe winter flounder Pleuronectes americanus. This peptide is of specific interest because it does not\nexhibit the canonical facially amphiphilic orientation of side chains when in a helical orientation.\nDifferent analogs of AP3 were synthesized in which length, charge identity, and Trp position were\nvaried to investigate the sequence-structure and activity relationship. We performed biophysical and\nmicrobiological characterization using fluorescence spectroscopy, CD spectroscopy, vesicle leakage\nassays, bacterial membrane permeabilization assays, and minimal inhibitory concentration (MIC)\nassays. Fluorescence spectroscopy showed that the peptides bind to lipid bilayers to similar extents,\nwhile CD spectra show the peptides adopt helical conformations. All five peptides tested in this study\nexhibited binding to model lipid membranes, while the truncated peptides showed no measurable\nantimicrobial activity. The most active peptide proved to be the parent peptide AP3 with the highest\ndegree of leakage and bacterial membrane permeabilization. Moreover, it was found that the ability\nto permeabilize model and bacterial membranes correlated most closely with the ability to predict\nantimicrobial activity.
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