Comparision of Membrane Interactions of Acylated and Non-Acylated Lactoferricins by Solid-State NMR Spectroscopy and Molecular Dynamics Simulations

Abstract

LfB6 (RRWQWR-NH2) is a tryptophan- and arginine-rich cationic antimicrobial peptide with broad spectrum activity derived from bovine lactoferrin. Membrane binding occurs via electrostatic interactions between arginines and negative charges on the bacterial cell membrane and intercalation of the tryptophans at the membrane interface. N-terminal acylation (CH3(CH2)4CO-RRWQWR-NH2; C6-LfB6) can enhance the antimicrobial activity (Greathouse et al. (2008) J. Pept. Sci. 14:1103). Solid-state 2H and 31P NMR spectroscopy combined with all-atom and coarse-grained molecular dynamics (CG-MD) simulations have confirmed subtle differences between 1 mol% LfB6 and C6-LfB in bilayers composed of 3:1 POPE:POPG (anionic, bacterial-like) and POPC (zwitterionic, mammalian-like). MD simulations reveal that the arginines of C6-LfB6 make first contact with POPE:POPG; whereas the C6 tails are first to contact POPC. LfB6 shows no sequence preference. Additionally, C6-LfB6 inserts more deeply than LfB6 into both membranes. Tryptophan emission fluorescence spectra suggest the tryptophans in LfB6 and C6-LfB6 are more water exposed in neutral compared to anionic membranes, while CG-MD simulations reveal that LfB6 comes off the POPC membrane, exposing the tryptophans to water. Acylation, therefore, increases the “stickiness” of the peptide for lipid bilayers. Although both peptides at 1 mol% show significant membrane effects during short range simulations, C6-LfB6 has less influence on lipid order. We now compare experimental and molecular dynamics results for LfB6 and C6- LfB6 at 4 mol%. Solid-state 2H NMR spectra indicate that C6-LfB6 has a greater effect on the lipid acyl chain order at 4 mol% compared to 1 mol%; whereas the effects of LfB6 are similar at both concentrations. Molecular dynamics simulations will be presented for comparison.