Characterization of Membrane Interactions with Lactoferricin Peptides by Both All-Atom and Coarse-Grained Molecular Dynamics Simulations, Solid-State NMR, and Fluorescence Spectroscopy

Abstract

LfB6 (RRWQWR-NH2) is a small cationic antimicrobial peptide with broad spectrum effectiveness that is derived from bovine lactoferrin. The mechanism for interaction between the antimicrobial peptide and the bacterial cell membrane is hypothesized to depend on lipid composition. Bacterial membranes generally contain a significant fraction of negatively charged lipids in contrast with zwitterionic mammalian membranes. Previously, we characterized the interactions of an acylated LfB6 (C6-LfB6) with a model bacterial membrane (3:1 POPE:POPG) and a model mammalian membrane (POPC). We observed that for C6-LfB6, the Arg residues lead the interaction with the POPE:POPG membrane, while the C6 tail is first to associate with the POPC membrane. Here, we investigate the interactions of the non-acylated LfB6 peptide with the same model membranes, using over 9 μs of all-atom molecular dynamics as well as 24 μs of coarse grained simulations and we compare our results to solid-state 2H and 31P NMR, and fluorescence spectroscopy. Molecular dynamics simulations reveal that the LfB6 peptide backbone does not penetrate as deeply in the model membranes as C6-LfB6. Further, both the arginines and tryptophans of LfB6 associate with both model membranes at the same time and the tryptophans of LfB6 are more deeply buried in the model mammalian membrane than with the acylated peptide. There is evidence in the simulation of hydrogen bonding to water by the tryptophans in both acylated and non-acylated peptides in spite of the low local water density and the burial depth found in the simulations. The results also show subtle changes in the membranes’ structure between the acylated and non-acylated peptides.