Biochemistry (Moscow), Supplement Series A: Membrane and Cell Biology最新文献

A growing number of studies points to the relationship between the development of neurodegenerative diseases and the structure and lipid composition of neuronal membranes. One of the structural elements of cell membranes, to which special attention is paid in this regard, are liquid-ordered lipid domains, or rafts. The study of rafts and age-related changes in the lipid composition of neuronal cells is becoming increasingly relevant and is constantly being updated. In this review, we tried to highlight the possible role of the lipid component of cell membranes, their structure, and physicochemical characteristics in the development of diseases associated with aging. Evidence is reviewed that supports a possible role of rafts in diseases that over a long period of time lead to disruption of the functioning of neurons. There is a reason to believe that the therapeutic effects of various molecules, such as lysolipids and gangliosides, are due to their physicochemical properties and are realized indirectly, through their influence on the organization of lipid domains in membranes. As the role of lipid domains and, in general, the mechanisms of interaction and mutual influence of the lipid composition and disease development are more fully understood, this knowledge can be used to develop new therapeutic or preventive methods to combat diseases associated with aging.

The ability of extracts of grapefruit seeds (ESG), sea buckthorn leaves (ESBL), and chaga (EC) to inhibit membrane fusion was evaluated. It was found that ESBL and EC inhibited Ca²⁺-mediated fusion of phosphatidylglycerol-enriched lipid vesicles; the inhibition indexes were about 90 and 100%, respectively. ESG did not inhibit the fusion of negatively charged liposomes induced by calcium. In addition to calcium-mediated liposome fusion, EC inhibited the fusion of vesicles from a mixture of phosphatidylcholine and cholesterol under the action of polyethylene glycol with a molecular weight of 8000 Da (the inhibition index was 80%). The other two extracts had no effect on polymer-induced fusion of uncharged membranes. The effect of some major components of the tested extracts on the fusion of vesicles was evaluated. It has been shown that flavonols, quercetin and myricetin, which are major components of ESBL, inhibited the fusion of negatively charged membranes under the action of calcium (the inhibition indexes were about 85 and 60%, respectively). Another flavonol of ESBL, the glycoside of quercetin rutin, did not have such an effect. The data obtained made it possible to relate the ESBL suppression of calcium-induced fusion of lipid vesicles with the presence of quercetin and myricetin in its composition. These flavonols had virtually no effect on polyethylene glycol-induced vesicle fusion, which is consistent with the absence of ESBL action on liposome fusion under the action of polymer. The ability of quercetin and myricetin to reduce the melting temperature of phosphatidylglycerol with saturated hydrocarbon chains and to increase the half-width of the peak corresponding to melting has been demonstrated. The observed correlation between the parameters characterizing the thermotropic behavior of the lipid in the presence of quercetin and myricetin and the index of inhibition of calcium-mediated liposome fusion by these compounds may indicate a relationship between the ability of flavonols to influence the packaging of membrane lipids and inhibit vesicle fusion. Pentacyclic triterpenoids, betulin and lupeol, which are part of EC, did not inhibit the fusion of vesicles under the action of both calcium and polyethylene glycol, and their presence in EC cannot be responsible for the antifusogenic activity of EC.

Antimicrobial activity of some amphipathic peptides is associated with the formation of through pores in bacterial membranes. Antimicrobial peptides (AMPs) specifically bind to the plasma membrane by incorporating their hydrophobic regions into the outer lipid monolayer. The membrane is inevitably deformed. Many AMPs form so-called toroidal pores, the edge of which is partially lined with peptide molecules. The edge of the pore is characterized by significant deformations. In this work, we calculated the energy of the pore edge, with amphipathic peptides located on the pore equator, as well as the energy of deformations induced by AMP in a planar lipid bilayer. It was shown that for certain physicochemical and geometric characteristics of the AMP molecule the energy of the pore, on the equator of which two or more peptide molecules are located, can be lower than the energy of deformations induced in the planar bilayer by the same number of peptide molecules. Thus, two AMP molecules can, in principle, form a through pore in the membrane, although this is possible only in a fairly narrow range of physicochemical and geometric characteristics of the peptides.

In non-excitable cells, IP3-driven Ca²⁺ release plays a pivotal role in agonist-induced Ca²⁺ signaling. The efficiency of the phosphoinositide cascade, which couples diverse cell surface receptors to Ca²⁺ mobilization, is modulated by a number of kinases, including phosphoinositide 3-kinase (PI3K) that phosphorylates PIP2 to generate the phospholipid PIP3. We have previously shown that the PI3K inhibitor wortmannin does not affect acetylcholine-induced Ca²⁺ signaling in HEK-293 cells, while PI828, a PI3K inhibitor of distinct chemical nature, completely suppressed cellular responses to the agonist. As a possible reason for the different effectivity of wortmannin and PI828, PI3K isoforms functioning in HEK-293 could be much more sensitive to PI828. To clarify this issue, we generated a monoclonal line of HEK-293 cell, which expresses two genetically encoded sensors, namely, cytosolic Ca²⁺ sensor R-GECO1 and PIP3 sensor PH(Akt)-Venus. The cells of this line allowed for simultaneous monitoring of Ca²⁺ signals and PI3K activity. While R-GECO1 fluorescence is directly stimulated by Ca²⁺ binding, generation of PIP3 by PI3K initiates the translocation of PH(Akt)-Venus from the cytosol to the plasmalemma. It turned out that acetylcholine initiated a transient increase in the intracellular Ca²⁺ but did not affect the distribution of the PIP3 sensor in the cell cytosol. This indicated that acetylcholine did not stimulate PI3K activity. At the same time, insulin, which stimulates PI3K through tyrosine kinase receptors, caused the cytosol/plasmalemma translocation of PH(Akt)-Venus, thus demonstrating insulin-induced PI3K activity. This insulin-evoked translocation of PH(Akt)-Venus was canceled by wortmannin and PI828, suggesting that the inhibition of PI3K activity by these compounds was rather effective. Thus, being capable of stimulating intracellular Ca²⁺ signaling in HEK-293 cells, acetylcholine did not stimulate the PI3K pathway, which, therefore, was not involved in cholinergic transduction. Although the inhibition of PI3K by wortmannin and PI828 was undoubtable, the results of the present work suggest that PI828 suppressed acetylcholine induced Ca²⁺ signaling nonspecifically, that is, not involving PI3K, but acting on some other cellular target.

The results of investigation of electrogenic transport by the Na⁺,K⁺-ATPase, the enzyme providing the active transport of Na⁺ and K⁺ ions through cell membrane, are reviewed. The main contribution to electric current generated through the functioning of the Na⁺,K⁺-ATPase is assigned to the movements of ions in access channels—the channel-like structures connecting the ion binding sites with the solutions. The electrogenic transport was studied in a model system consisting of a bilayer lipid membrane with adsorbed membrane fragments containing the Na⁺,K⁺-ATPase. The impedance method applied to this study allowed the investigation of access channels in the Na⁺,K⁺-ATPase. The review notes a significant contribution of Yu.A. Chizmadzhev to the development of the theoretical model of transport processes in the Na⁺,K⁺-ATPase.

Various amphipathic antimicrobial peptides (AMPs) kill bacteria by forming through pores in plasma membranes. Previously, at least two alternative types of hypotheses about the mechanisms of AMP membrane poration were put forward. The so-called “non-local” models suggest that AMPs, when interacting with a membrane, modify its integral elastic characteristics, in particular, lateral tension, which leads to a decrease in the deformation energy during pore formation. In this case, AMP molecules can be located far from the formed pore. In “local” models, it is assumed that pores are formed in the immediate vicinity of single AMP molecules or their aggregates, while the peptides partially or completely line the edge of the pore. In both types of models, it is assumed that the process of pore formation passes via an intermediate structure, the so-called hydrophobic defect. In this work, we calculated the energy of formation of the hydrophobic defect in the membrane with adsorbed AMP molecules under the assumption of the non-local poration mechanism. It was found that AMPs actually lower the energy of the hydrophobic defect. However, this decrease in energy is insufficient to explain the experimentally observed average waiting time for membrane poration. Thus, it can be concluded that amphipathic peptides form pores in membranes predominantly by the local mechanism, directly participating in the formation of the pore edge, although nonlocal effects of AMP–membrane interaction somewhat facilitate poration of the membrane as a whole.

Classical theory of fusion considers the fusion of bilayer membranes as a unification of the material of the membranes themselves and the water volumes surrounded by them. It has been shown that membrane fusion is accompanied by significant deformation of lipid monolayers. The optimal trajectory of the process passes through several intermediate structures characterized by local minima of the free energy of the system; the minima are separated by energy barriers. The key fusion intermediate is stalk, where the contacting membrane monolayers have already fused, but the distal monolayers have not yet, and hemifusion diaphragm, a structure with an extended lipid bilayer formed by two distal monolayers of merging membranes located in the center between the radially displaced fused contact monolayers. In this work, we consider fusion of a bilayer membrane and a lipid monolayer located at the water–triolein interface from the standpoint of the classical theory of fusion. An intermediate π-shaped structure, formed as a result of a lipid droplet monolayer and a peroxisome bilayer fusion, was considered, and the dependence of its energy on the geometric parameters and elastic characteristics of the system was analyzed. In particular, it was shown that the π‑shaped structure is similar to the hemifusion diaphragm of the classical theory of bilayer membrane fusion: an increase in the radial dimensions of both structures becomes more energetically favorable with a decrease in the spontaneous curvature of the membrane monolayers. This result is consistent with the available experimental data on the fusion of lipid droplets with peroxisomes.