title: Molecular electrometer and binding of cations to phospholipid bilayers.
abstract: Despite the vast amount of experimental and theoretical studies on the binding affinity of cations - especially the biologically relevant Na+and Ca2+- for phospholipid bilayers, there is no consensus in the literature. Here we show that by interpreting changes in the choline headgroup order parameters according to the 'molecular electrometer' concept [Seelig et al., Biochemistry, 1987, 26, 7535], one can directly compare the ion binding affinities between simulations and experiments. Our findings strongly support the view that in contrast to Ca2+and other multivalent ions, Na+and other monovalent ions (except Li+) do not specifically bind to phosphatidylcholine lipid bilayers at sub-molar concentrations. However, the Na+binding affinity was overestimated by several molecular dynamics simulation models, resulting in artificially positively charged bilayers and exaggerated structural effects in the lipid headgroups. While qualitatively correct headgroup order parameter response was observed with Ca2+binding in all the tested models, no model had sufficient quantitative accuracy to interpret the Ca2+:lipid stoichiometry or the induced atomistic resolution structural changes. All scientific contributions to this open collaboration work were made publicly, using nmrlipids.blogspot.fi as the main communication platform.
authors.affiliation: School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK.
authors.forename: Andrea
authors.initials: A
authors.lastname: Catte
authors.affiliation: Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland. samuli.ollila@aalto.fi.
authors.forename: Mykhailo
authors.initials: M
authors.lastname: Girych
authors.affiliation: Department of Physics, Tampere University of Technology, Tampere, Finland and Department of Physics, University of Helsinki, Helsinki, Finland.
authors.forename: Matti
authors.initials: M
authors.lastname: Javanainen
authors.affiliation: Univ Lyon, Université Claude Bernard Lyon 1, CNRS, Institut Lumiére Matiére, F-69622, LYON, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Loison
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 16610 Prague 6, Czech Republic and Charles University in Prague, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16 Prague 2, Czech Republic.
authors.forename: Josef
authors.initials: J
authors.lastname: Melcr
authors.affiliation: Fachbereich Physik, Freie Universität Berlin, Berlin, Germany and Max Planck Institute of Colloids and Interfaces, Department of Theory and Bio-Systems, Potsdam, Germany.
authors.forename: Markus S
authors.initials: MS
authors.lastname: Miettinen
authors.affiliation: Institut de Biologie et Chimie des Protéines (IBCP), CNRS UMR 5086, Lyon, France.
authors.forename: Luca
authors.identifier: http://orcid.org/0000-0002-6352-4595
authors.initials: L
authors.lastname: Monticelli
authors.affiliation: Department of Chemistry, Aalto University, Espoo, Finland.
authors.forename: Jukka
authors.initials: J
authors.lastname: Määttä
authors.affiliation: School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK.
authors.forename: Vasily S
authors.initials: VS
authors.lastname: Oganesyan
authors.affiliation: Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland. samuli.ollila@aalto.fi.
authors.forename: O H Samuli
authors.initials: OH
authors.lastname: Ollila
authors.affiliation: Department of Physics, Tampere University of Technology, Tampere, Finland.
authors.forename: Joona
authors.initials: J
authors.lastname: Tynkkynen
authors.affiliation: Univ Lyon, Université Claude Bernard Lyon 1, CNRS, Institut Lumiére Matiére, F-69622, LYON, France.
authors.forename: Sergey
authors.initials: S
authors.lastname: Vilov
mesh_terms: D002118:Calcium / Q000737:chemistry; D002412:Cations / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D010713:Phosphatidylcholines / Q000737:chemistry*; D012964:Sodium / Q000737:chemistry
chemical_list: D002412:Cations; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D012964:Sodium; D002118:Calcium