Membrane-Embedded Nanoparticles Induce Lipid Rearrangements Similar to Those Exhibited by Biological Membrane Proteins

Abstract

Amphiphilic monolayer-protected gold nanoparticles (NPs) have recently been shown to spontaneously fuse with lipid bilayers under typical physiological conditions. The final configuration of these NPs after fusion is proposed to be a bilayer-spanning configuration resembling transmembrane proteins. In this work, we use atomistic molecular dynamics simulations to explore the rearrangement of the surrounding lipid bilayer after NP insertion as a function of particle size and monolayer composition. All NPs studied induce local bilayer thinning and a commensurate decrease in local lipid tail order. Bilayer thickness changes of similar magnitude have been shown to drive protein aggregation, implying that NPs may also experience a membrane-mediated attraction. Unlike most membrane proteins, the exposed surface of the NP has a high charge density that causes electrostatic interactions to condense and reorient nearby lipid head groups. The decrease in tail order also leads to an increased likelihood of lipid tails spontaneously protruding toward solvent, a behavior related to the kinetic pathway for both NP insertion and vesicle–vesicle fusion. Finally, our results show that NPs can even extract lipids from the surrounding bilayer to preferentially intercalate within the exposed monolayer. These drastic lipid rearrangements are similar to the lipid mixing encouraged by fusion peptides, potentially allowing these NPs to be tuned to perform a similar biological function. This work complements previous studies on the NP–bilayer fusion mechanism by detailing the response of the bilayer to an embedded NP and suggests guidelines for the design of nanoparticles that induce controllable lipid rearrangements