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Phosphatidic Acid Domains in Membranes: Effect of Divalent Counterions

AuthorsFaraudo, Jordi ; Travesset, Alex
Phosphatidic acid (PA)
Membrane fusion
Divalent ions
Binding constants
Charge inversion
Interfacial water
Molecular dynamics simulations
Issue Date26-Jan-2007
PublisherRockefeller University Press
CitationBiophysical Journal 92(8): 2806-2818 (2007)
AbstractPhosphatidic acid (PA) is emerging as a key phospholipid in a wide range of biological processes such as signal transduction, secretion, or membrane fusion. In most cases, the biological functionality of PA is associated with the presence of micromolar to millimolar calcium concentrations. It has been argued that PA can create defects in the packing of lipids in membranes due to lateral phase separation by divalent ions, which in turn aggregate proteins with high affinity for PA. In this article, we present a detailed investigation of the properties of PA domains in the presence of divalent ions by a combination of molecular dynamics simulations and theoretical methods. Our results show that PA is extremely effective in binding divalent ions through its oxygen atoms, with a broad distribution of binding constants and exhibiting the phenomenon of charge inversion (a total number of bound counterion charges that exceeds the negative PA charge). We predict that a PA-rich domain undergoes a drastic reorganization when divalent cations reach micromolar concentrations (i.e., typical physiological conditions), as PA lipids become doubly charged by releasing their protons. We also present a detailed investigation of the properties of interfacial water, which determine the binding of proteins or other molecules. We conclude with a discussion of the implications of our results in the context of recent experimental studies in model systems and in real cells.
Description13 pages, 11 figures.-- PMCID: PMC1831684.-- Printed version published on Apr 2007.
Publisher version (URL)http://dx.doi.org/10.1529/biophysj.106.092015
Appears in Collections:(ICMAB) Artículos
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