Decoupling membrane permeabilization and antimicrobial activity in amphipathic peptides

Abstract

The prevailing model of cathelicidin function holds that peptide helicity leads to membrane permeabilization, which in turn leads to killing of gram-negative bacteria. Using a paired Ala-Aib mutagenesis approach to isolate sidechain and structure-dependent functions, we demonstrate here that the effect of helicity on gram-negative killing in a model cathelicidin-derived scaffold is species-dependent. We then leverage this insight to derive lead compounds with up to 32-fold improvements in selectivity for bacterial over mammalian cells. Further interrogation of the mechanistic basis for selectivity demonstrates that, while helicity may predict permeabilization, permeabilization does not predict killing of gram-negative bacteria. Thus, neither helicity nor permeabilization is a universal requirement for cathelicidin-mediated killing.