Designed peptide with a flexible central motif from ranatuerins adapts its conformation to bacterial membranes

The long-standing goal in the field of peptide antibiotics has been to design lead compounds that have a wide spectrum of excellent antibacterial activity but are nontoxic to human cells. Gram-negative and Gram-positive bacteria have very different membranes, which are additionally modified in some drug-resistant species, presenting a challenge for the design of a single membrane-active peptide able to adapt its conformation to various physical properties of membrane microenvironments. In this paper, we describe how a peptide sequence can be constructed starting from an adaptable dynamic turn tandem motif in a central location. The peptide, named flexampin, has been examined firstly by molecular dynamics simulations. It uses a flexible central motif and designed helix-forming cationic amphipathic arms to form a boomerang-like, L-shape, V-shape, and hairpin, super-secondary structures, whichever is the best in matching amphipathic and hydrophobic microenvironments it encounters. Secondly, activity measurements showed that flexampin is bactericidal at low micromolar concentrations against Gram-positive and Gram-negative strains including some multidrug resistant clinical isolates, while it is nontoxic for human circulating blood cells, does not cause DNA damage, and has good selectivity for bacterial cells in comparison to human cells. It is the first membrane-active peptide designed with the ability to self-adjust the orientation of its two cationic helical arms, 3D-hydrophobic moment, and dipole moment for obtaining a better grasp of anionic polar head groups at bacterial membrane surfaces.