Osmotic Stress Induced Desorption of Calcium Ions from Dipolar Lipid Membranes

Abstract

The interaction between multivalent ions and lipid membranes with saturated tails and dipolar (net neutral) headgroups can lead to adsorption of the ions onto the membrane. The ions charge the membranes and contribute to electrostatic repulsion between them, in a similar manner to membranes containing charged lipids. Using solution X-ray scattering and the osmotic stress method, we measured and modeled the pressure-distance curves between partially charged membranes containing mixtures of charged (1,2-dilauroyl-sn-glycero-3-phospho-l-serine, DLPS) and dipolar (1,2-dilauroyl-sn-glycero-3-phosphocholine, DLPC) lipids over a wide range of membrane charge densities. We then compared these pressure-distance curves with those of DLPC membranes in the presence of 10 mM CaCl. Our data and modeling show that when low osmotic stress is applied to the DLPC bilayers, the membrane charge density is equivalent to that of a charged membrane containing ca. 4 mol % DLPS and 96 mol % DLPC. As the osmotic stress increased, the charge density of the DLPC membrane decreased and resembled that of a membrane containing ca. 1 mol % DLPS. These data are consistent with desorption of the calcium ions from the DLPC membrane with increasing osmotic stress.

D+: software for high-resolution hierarchical modeling of solution X-ray scattering from complex structures

“…Solution X-ray scattering measurements were performed using an energy of 10 keV at the ID02 beamline (headed by T. Narayanan) of ESRF (Grenoble), at the P12 EMBL BioSAXS beamline (D. Svergun) of PETRA III (DESY, Hamburg) and at the SWING beamline (J. Perez) of the Soleil synchrotron (Gif-sur-Yvette), or with our inhouse spectrometer, using an energy of 8 keV. Detailed experimental descriptions of these setups were provided elsewhere (David & Pé rez, 2009;Blanchet et al, 2015;Van Vaerenbergh et al, 2016;Nadler et al, 2011;Louzon et al, 2017;Fink et al, 2017). The intensity frames were normalized to the intensity of the transmitted beam, azimuthally averaged (Hammersley, 2016) and background subtracted as explained below, in SOM Section 5 and in our earlier publications (Ginsburg et al, 2016(Ginsburg et al, , 2017.…”

“…The challenge of structural biophysics is to determine the high-resolution structure of large self-assembled complexes, made of many subunits, in their biologically relevant solution conditions. Solution small-and wide-angle X-ray scattering (SAXS/WAXS) methods are one of the important label-free and highly sensitive bulk methods for investigating the structure of and interactions between complex molecular constructs (Rä dler et al, 1997;Koltover et al, 1998;Schilt et al, 2016;Dvir et al, 2013Dvir et al, , 2014Chung et al, 2015Chung et al, , 2016Lotan et al, 2016;Ojeda-Lopez et al, 2014;Moshe et al, 2013;Saper et al, 2012;Steiner et al, 2012;Szekely, Schilt et al, 2011;Nadler et al, 2011;Choi et al, 2009Choi et al, , 2016Wong et al, 2000;Deek et al, 2013;Beck et al, 2010;Kornreich et al, 2016;Shaharabani et al, 2016;Ginsburg et al, 2017;Asor et al, 2017;Fink et al, 2017). With modern synchrotron facilities the temporal and spatial resolution of these methods has been greatly improved (Ginsburg et al, 2016;Kler et al, 2012).…”

D+: Software for High-Resolution Hierarchical Modeling of Solution X-Ray Scattering from Complex Structures

“…The challenge of structural biophysics is to determine the high-resolution structure of large self-assembled complexes, made of many subunits, in their biologically relevant solution conditions. Solution small-and wide-angle X-ray scattering (SAXS/WAXS) methods are one of the important labelfree and highly sensitive bulk methods for investigating the structure and interactions between complex molecular constructs (Rädler et al, 1997;Koltover et al, 1998;Schilt et al, 2016;Dvir et al, 2014;Dvir et al, 2013;Chung et al, 2015;Chung et al, 2016;Lotan et al, 2016;Ojeda-Lopez et al, 2014;Moshe et al, 2013;Saper et al, 2012;Steiner et al, 2012;Szekely et al, 2011a;Szekely et al, 2011b;Choi et al, 2009;Choi et al, 2016;Wong et al, 2000;Deek et al, 2013;Beck et al, 2010;Kornreich et al, 2016;Shaharabani et al, 2016;Ginsburg et al, 2017;Asor et al, 2017;Fink et al, 2017a). With modern synchrotron facilities the temporal and spatial resolution of these methods has been greatly improved Kler et al, 2012).…”

Interacting Bacteria Surfaces

“…The structure and interactions between biomolecular assemblies, including biopolymers, filamentous protein networks, lipid membranes, or lipidbiopolymer complexes, have been extensively studied using solution x-ray or neutron scattering and the osmotic stress method (1)(2)(3)(4)(5)(6). Osmotic stress is often applied by an external polymer solution, which is in contact with the investigated solution (or dispersion) through a semipermeable membrane (made of cellulose, for example).…”