Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2003 Nov;85(5):3120-31.
doi: 10.1016/S0006-3495(03)74730-4.

Mixed bilayer containing dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine: lipid complexation, ion binding, and electrostatics

Sagar A Pandit  1 , David Bostick, Max L Berkowitz
Affiliations

Mixed bilayer containing dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine: lipid complexation, ion binding, and electrostatics

Sagar A Pandit et al. Biophys J. 2003 Nov.

Abstract

Two mixed bilayers containing dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine at a ratio of 5:1 are simulated in NaCl electrolyte solutions of different concentration using the molecular dynamics technique. Direct NH.O and CH.O hydrogen bonding between lipids was observed to serve as the basis of interlipid complexation. It is deduced from our results and previous studies that dipalmitoylphosphatidylcholine alone is less likely to form interlipid complexes than in the presence of bound ions or other bilayer "impurities" such as dipalmitoylphosphatidylserine. The binding of counterions is observed and quantitated. Based upon the calculated ion binding constants, the Gouy-Chapman surface potential (theta) is calculated. In addition we calculated the electrostatic potential profile (Phi) by twice integrating the system charge distribution. A large discrepancy between and the value of Phi at the membrane surface is observed. However, at "larger" distance from the bilayer surface, a qualitative similarity in the z-profiles of Phi and psi(GC) is seen. The discrepancy between the two potential profiles near the bilayer surface is attributed to the discrete and nonbulk-like nature of water in the interfacial region and to the complex geometry of this region.

PubMed Disclaimer

Figures

FIGURE 1
FIGURE 1
Structures of the simulated DPPS (PS) and DPPC (PC) molecules. The atom naming is adopted from a previous convention (Smondyrev and Berkowitz, 1999).
FIGURE 2
FIGURE 2
Time series data of the centers of mass of the ions in both systems.
FIGURE 3
FIGURE 3
Distribution of the angle between formula image (the vector pointing from the headgroup phosphorus atom to the headgroup nitrogen atom) and the outwardly directed bilayer normal for each lipid in both systems.
FIGURE 4
FIGURE 4
Schematic diagram showing the established criteria for NH···O and CH···O hydrogen bonding.
FIGURE 5
FIGURE 5
Distribution of the number of lipids bound to a given lipid via direct bonding for each PC and PS in both systems.
FIGURE 6
FIGURE 6
Distribution of the number of lipids bound to a given lipid via direct bonding in a pure DPPC system with and without salt.
FIGURE 7
FIGURE 7
Distribution of different types of direct hydrogen bonding for “smaller” and “larger” lipid complexes for both lipid types in both simulated systems.
FIGURE 8
FIGURE 8
Snapshots showing complexation of lipids. A schematic representation of each complex is also shown. In the representations, blue arrows represent PS, black arrows represent PC, and red lines represent the interlipid direct hydrogen bonds. The arrowheads correspond to the nitrogen atom of the headgroup.
FIGURE 9
FIGURE 9
Distribution of the number of lipids bound to a single cation for both cation species in both systems.
FIGURE 10
FIGURE 10
Snapshots of complexes involving an ion bridge. Na+ (blue sphere) is coordinated with two PC lipids and two PS lipids (left). formula image is coordinated with four lipids via hydrogen bonds (right).
FIGURE 11
FIGURE 11
Various quantities as a function of z in the S2 system: (a) hydration level of each ion type, (b) densities of various atom types, and (c) number of ions of each type.
FIGURE 12
FIGURE 12
Various quantities as a function of z in the S1 system: (a) hydration level of each ion type, (b) densities of various atom types, and (c) number of ions of each type.
FIGURE 13
FIGURE 13
(a) Total electrostatic potential profile of the S2 system as a function of z. (b) Density profile of co- and counterions as a function of z in the S2 system.
FIGURE 14
FIGURE 14
(a) Total electrostatic potential profile of the S1 system as a function of z. (b) Density profile of co- and counterions as a function of z in the S1 system.
See this image and copyright information in PMC

References

    1. Berendsen, H., D. van der Spoel, and R. van Drunen. 1995. GROMACS: a message-passing parallel molecular dynamics implementation. Comp. Phys. Comm. 91:43–56.
    1. Berger, O., O. Edholm, and F. Jahnig. 1997. Molecular dynamics simulations of a fluid bilayer of dipalmitoylphosphatidylcholine at full hydration, constant pressure, and constant temperature. Biophys. J. 72:2002–2013. - PMC - PubMed
    1. Boda, D., K.-Y. Chan, and D. Henderson. 1998. Monte Carlo simulation of an ion-dipole mixture as a model of an electrical double layer. J. Chem. Phys. 109:7362–7371.
    1. Boda, D., D. Henderson, A. Patrykiejew, and S. Sokolowski. 2000. Simulation and density functional study of simple membrane. II. Solvent effects using the solvent primitive model. J. Chem. Phys. 113:802–806.
    1. Boda, D., D. Henderson, R. Rowley, and S. Sokolowski. 1999. Simulation and density functional study of a simple membrane separating two restricted primitive model electrolytes. J. Chem. Phys. 111:9382–9388.

Publication types

LinkOut - more resources