Antimicrobial Peptides: Correlation Between Pore Forming Potency in Lipid Vesicles and Antimicrobial, Hemolytic and Cytotoxic Activity

Abstract

The rapid rise in drug-resistant pathogenic microorganisms has generated elevated interest in antimicrobial peptides (AMPs), which have been proposed to act largely based on the potential to induce target cell membrane permeabilization. To search for novel AMPs, we designed a 26-residue combinatorial peptide library which was screened for potent membrane pore-formers using a lipid-vesicle-based leakage assay. Selected pore-forming peptides also showed good antimicrobial activity against yeast, gram-positive and gram-negative bacteria. To determine if peptides with higher activity could be identified with the same principle, we used one of the original selected peptides as a template, to design a combinatorial peptide library iteration. This iterative library was screened using a recently modified orthogonal fluorescence-based liposome assay that specifically selects for peptides that can induce highly potent, long-lived pores. The peptides in the iterative library, which had an average pore forming activity that was significantly higher than the ones in the original library, was consequently screened at a much higher stringency to find the most potent members. We identified a conserved family of sequences with extremely high membrane permeabilizing activity against lipid vesicles. These selected positives from the iteration library screen were synthesized and tested in antimicrobial and hemolytic assays. Despite their much higher vesicle permeabilization activity, their antimicrobial activities are only slightly better than the positives identified in the original library. These results support the idea that antimicrobial activity is a complex bioactivity with important factors that extend beyond the simple concept of membrane permeabilization.