NaCl Interactions with Phosphatidylcholine Bilayers Do Not Alter Membrane Structure but Induce Long-Range Ordering of Ions and Water

NaCl Interactions with Phosphatidylcholine Bilayers Do Not Alter Membrane Structure but Induce... It is generally accepted that ions interact directly with lipids in biological membranes. Decades of biophysical studies on pure lipid bilayer systems have shown that only certain types of ions, most significantly large anions and multivalent cations, can fundamentally alter the structure and dynamics of lipid bilayers. It has long been accepted that at physiological concentrations NaCl ions do not alter the physical behavior or structure of bilayers composed solely of zwitterionic phosphatidylcholine (PC) lipids. Recent X-ray scattering experiments have reaffirmed this dogma, showing that below 1 M concentration, NaCl does not significantly alter bilayer structure. However, despite this history, there is an ongoing controversy within the molecular dynamics (MD) simulation community regarding NaCl/PC interactions. In particular, the CHARMM and GROMOS force fields show dramatically different behavior, including the effect on bilayer structure, surface potential, and the ability to form stable, coordinated ion–lipid complexes. Here, using long-timescale, constant-pressure simulations under the newest version of the CHARMM force field, we find that Na+ and Cl− associate with PC head groups in a POPC bilayer with approximately equal, though weak, affinity, and that the salt has a negligible effect on bilayer structure, consistent with earlier CHARMM results and more recent X-ray data. The results suggest that interpretation of simulations where lipids interact with charged groups of any sort, including charged proteins, must be carefully scrutinized. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

NaCl Interactions with Phosphatidylcholine Bilayers Do Not Alter Membrane Structure but Induce Long-Range Ordering of Ions and Water

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Publisher
Springer-Verlag
Copyright
Copyright © 2011 by Springer Science+Business Media, LLC
Subject
Life Sciences; Human Physiology; Biochemistry, general
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-011-9395-1
Publisher site
See Article on Publisher Site

Abstract

It is generally accepted that ions interact directly with lipids in biological membranes. Decades of biophysical studies on pure lipid bilayer systems have shown that only certain types of ions, most significantly large anions and multivalent cations, can fundamentally alter the structure and dynamics of lipid bilayers. It has long been accepted that at physiological concentrations NaCl ions do not alter the physical behavior or structure of bilayers composed solely of zwitterionic phosphatidylcholine (PC) lipids. Recent X-ray scattering experiments have reaffirmed this dogma, showing that below 1 M concentration, NaCl does not significantly alter bilayer structure. However, despite this history, there is an ongoing controversy within the molecular dynamics (MD) simulation community regarding NaCl/PC interactions. In particular, the CHARMM and GROMOS force fields show dramatically different behavior, including the effect on bilayer structure, surface potential, and the ability to form stable, coordinated ion–lipid complexes. Here, using long-timescale, constant-pressure simulations under the newest version of the CHARMM force field, we find that Na+ and Cl− associate with PC head groups in a POPC bilayer with approximately equal, though weak, affinity, and that the salt has a negligible effect on bilayer structure, consistent with earlier CHARMM results and more recent X-ray data. The results suggest that interpretation of simulations where lipids interact with charged groups of any sort, including charged proteins, must be carefully scrutinized.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Oct 21, 2011

References

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