Acylated Lactoferrin Peptides Using Solid State NMR and All-Atom Molecular Dynamics Simulations

Abstract

Lactoferricin B is a cationic antimicrobial peptide with broad spectrum effectiveness. A small piece extracted from this peptide, LfB6 (RRWQWR-NH2), has similar antimicrobial properties, which can be further enhanced by attaching a short fatty acid to the N-terminus (C6-LfB6). The exact mechanism by which antimicrobial peptides interact with bacterial cell membranes is not well understood, but it is proposed to depend on lipid composition. In contrast to mammalian membranes which are comprised primarily of neutral lipids, bacterial membranes contain a significant (∼20-25%) fraction of negatively charged lipids. In the case of LfB6, the presence of two tryptophans and three arginines are thought to promote selective interaction with bacterial cell membranes. Here, we investigate the interactions of C6-LfB6 with lipid bilayers by combining solid state 2H and 31P NMR with an ensemble of all-atom molecular dynamics simulations running in aggregate more than 10 microseconds. In particular, we have investigated the peptides interactions with bilayers with two distinct compositions: 3:1 POPE:POPG (bacteria-like) and POPC (mammal-like). The results show that at low concentration the peptide has very little effect on the acyl chain concentration of the anionic membrane, and a more substantial effect on the zwitterionic POPC membrane. The synergy between the experimental and simulation results generates new insights into the molecular-level physics driving antimicrobial function.