Grafting Charged Species to Membrane-Embedded Scaffolds Dramatically Increases the Rate of Bilayer Flipping

TitleGrafting Charged Species to Membrane-Embedded Scaffolds Dramatically Increases the Rate of Bilayer Flipping
Publication TypeJournal Article
Year of Publication2017
AuthorsVan Lehn, RC, Alexander-Katz, A
JournalAcs Central Science
Volume3
Issue3
Pagination186 - 195
Date Published2017/03/22/
ISBN Number2374-7943
Keywordsbiological-membranes, cation-pi interactions, force-field, gold nanoparticles, in-vitro, lipid-bilayers, molecular-dynamics simulations, monolayer-protected nanoparticles, protein topology, side-chain
Abstract

The cell membrane is a barrier to the passive diffusion of charged molecules due to the chemical properties of the lipid bilayer. Surprisingly, recent experiments have identified processes in which synthetic and biological charged species directly transfer across lipid bilayers on biologically relevant time scales. In particular, amphiphilic nanopartides have been shown to insert into lipid bilayers, requiring the transport of charged species across the bilayer. The molecular factors facilitating this rapid insertion process remain unknown. In this work, we use atomistic molecular dynamics simulations to calculate the free energy barrier associated with "flipping" charged species across a lipid bilayer for species that are grafted to a membrane -embedded scaffold, such as a membrane -embedded nanoparticle. We find that the free energy barrier for flipping a grafted ligand can be over 7 kcal/mol lower than the barrier for translocating an isolated, equivalent ion, yielding a S order of magnitude decrease in the corresponding flipping time scale. Similar results are found for flipping charged species grafted to either nanoparticle or protein scaffolds. These results reveal new mechanistic insight into the flipping of charged macromolecular components that might play an important, yet overlooked, role in signaling and charge transport in biological settings. Furthermore, our results suggest guidelines for the design of synthetic materials capable of rapidly flipping charged moieties across the cell membrane.

Short TitleACS Central Sci.