ИСТИНА

Lipid matrix of biological membranes consist from phospholipids with headgroups that can be uncharged (PC, PE etc.) or have a negative charge (PS, CL). Ionized polar groups make a significant input to potential drop at the membrane interface, boundary potential, φb. Two components of this electric field have a different physical nature. Diffuse part of the electrical double layer (EDL) located close to membrane surface corresponds to a surface potential, φs, and consists of hydrogen dissociated from headgroups and inorganic ions of the media. Dipole moments of lipid moieties together with associated water molecules are oriented at the membrane-water interface and create the dipole component of boundary potential, φd. Generally, some ions and small charged molecules may penetrate to the polar area of the membrane and contribute to this component as well. Several experimental techniques shortly presented in the review used to control both components of φb: electrokinetic measurements sensitive to φs, technique of planar lipid membranes and Langmuir monolayers detected any changes in the total φb. Their difference reports on φd component and reflects some structure reorganization in lipid bilayers induced by various membrane active agents, especially, by multivalent cations or positively charged polypeptides (i.e. polylysine). Gouy-Chapman model of EDL supply the quantitative description of electrostatic phenomena in simple systems with inorganic ions. The analytic model for charged macromolecules adsorbed at membrane surface currently developed in our laboratory. Our previous studies considers the significant changes of dipole potential (up to 150 mV) by adsorption of Gd3+ and Be2+ cations with a high-affinity to lipid membranes, if the negatively charged phosphatidylserine (PS, CL) presents in their composition. These observation correlate with data of calorymetry and compressibility of lipid monolayers detected a lateral condensation of PS in the presence of multivalent cations. Molecular dynamic simulations visualized this phenomenon at the molecular level and show micro-cluster of PS formation by adsorbed multivalent cations and polypeptides, which participate in the lateral compressibility of lipid membrane. So, it well explain the blocking effect Gd3+ on mechanosensitive channels of E.coli reconstituted into artificial lipid membrane composed from the mixture of PS/PC [1]. Tight coordination between neighbor PS molecules follows from MD simulations in the presence of Be2+. Experiments with artificial PS-coated silica beads or aged erythrocytes suggest that Be2+ can displace Ca2+ from headgroups of PS. This effect may mask them from Ca2+ -mediated recognition by PS-receptors that potentially prevent normal phagocytosis [2]. It seems to be significant for initial steps of membrane transformation in apoptotic cells and may results in some dangerous chronic inflammation. References: 1.Ermakov Y.A., Kamaraju K., Sengupta K., Sukharev S. Gadolinium ions block mechanosensitive channels by altering the packing and lateral pressure of anionic lipids. Biophys J. 98, 2010, 1018-1027. 2. Ermakov Yu., Kamaraju K., Dunina-Barkovskaya A., Vishnyakova K., Egorov Y., Anishkin A., Sukharev S. Highaffinity Interactions of Beryllium (2+) with Phosphatidylserine Result in a Cross-linking Effect Reducing Surface Recognition of the Lipid, Biochemistry. 56, 2017, 5457-5470. Acknowledgements: The study is supported by RFBR (No 16-04-00556-А)