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

Fluctuations of the ion current in elastic nanopores are studied in a wide frequency range and a complete description of their noise characteristics is presented. The lumen of ultrashort (<200 nm) lipid nanotubes (usNT) filled with an electrolyte solution was used as a model of an elastic nanopore. It is shown that at low frequencies (f < 300 Hz) the 1/f noise type prevails. This low frequency noise was analyzed at different salt concentrations and nanopore geometries and it was found that the 1/f noise power is proportional to the reciprocal of the number of charge carriers, which is in good agreement with the empirical Hooge relation. Linear approximation showed that the Hooge parameter for elastic nanopores is (2.5 ± 0.5) × 10^–3, which turned out to be an order of magnitude higher than for solid analogs. In the high-frequency regime (f > 1 kHz), white noise becomes dominant, the power density of which depends linearly on the signal bandwidth and, as the length of the usNT decreases and the ionic strength increases, it is in good agreement with its representation as the sum of the Johnson–Nyquist thermal noise and the Schottky shot noise.

Over the past few years, the attention of the whole world has been riveted to the emergence of new dangerous strains of viruses, among which a special place is occupied by coronaviruses that have overcome the interspecies barrier in the past 20 years: SARS viruses (SARS), Middle East respiratory syndrome (MERS), as well as a new coronavirus infection (SARS-CoV-2), which caused the largest pandemic since the Spanish flu in 1918. Coronaviruses are members of a class of enveloped viruses that have a lipoprotein envelope. This class also includes such serious pathogens as human immunodeficiency virus (HIV), hepatitis, Ebola virus, influenza, etc. Despite significant differences in the clinical picture of the course of disease caused by enveloped viruses, they themselves have a number of characteristic features, which determine their commonality. Regardless of the way of penetration into the cell—by endocytosis or direct fusion with the cell membrane—enveloped viruses are characterized by the following stages of interaction with the target cell: binding to receptors on the cell surface, interaction of the surface glycoproteins of the virus with the membrane structures of the infected cell, fusion of the lipid envelope of the virion with plasma or endosomal membrane, destruction of the protein capsid and its dissociation from the viral nucleoprotein. Subsequently, within the infected cell, the newly synthesized viral proteins must self-assemble on various membrane structures to form a progeny virion. Thus, both the initial stages of viral infection and the assembly and release of new viral particles are associated with the activity of viral proteins in relation to the cell membrane and its organelles. This review is devoted to the analysis of physicochemical mechanisms of functioning of the main structural proteins of a number of enveloped viruses in order to identify possible strategies for the membrane activity of such proteins at various stages of viral infection of the cell.

The effect of high concentrations of glutamate (Glu) on primary cultures of neurons from the rat brain led to a strong depolarization of mitochondria, which developed synchronously with a secondary increase in the intracellular free Ca²⁺ concentration (delayed calcium deregulation, DCD). Simultaneously with measurements of the intracellular free Ca²⁺ concentration ([Ca²⁺]_i), pH was measured in the mitochondrial matrix (pH_m) and cytosol (pH_c) of neurons when exposed to a toxic dose of Glu (100 µM). For this purpose, pH-sensitive green fluorescent protein mtYFP in mitochondria and pH-sensitive red fluorescent protein mKate in cytosol were expressed in primary cultures from the hippocampus of newborn rats. The resulting neuronal culture was loaded with the Ca²⁺ indicator Fura-FF; [Ca²⁺]_i, pH_m and pH_c were simultaneously measured in those neurons that expressed both mtYFP and mKate. It was found that during the first phase of the [Ca²⁺]_i response to Glu, when partial depolarization of mitochondria was observed, there was an increase in the pH gradient between the mitochondrial matrix and the cytosol (ΔpH), which compensated for the decrease in the electrical component of the mitochondrial potential (∆Ψ_m), thereby maintaining the constancy of the electrochemical potential of mitochondria. The development of DCD led to an abrupt decrease in ∆Ψ_m and ΔpH in the soma of neurons; however, a complete collapse of ΔpH was not observed. This may mean that DCD was not caused by a nonspecific megapore in the inner mitochondrial membrane (mPTP), as is commonly believed. Alternatively, part of the mitochondria in the soma of neurons could retain the barrier properties of the inner membrane and did not form mPTP even with the development of DCD and reaching a high [Ca²⁺]_i plateau.

Photodynamic impact on neurons and glial cells, causing oxidative stress and ischemic damage, is accompanied by disruption of calcium homeostasis and activation or suppression of diverse calcium-dependent mechanisms, such as calcium pumps and channels, calcium-dependent signaling or executive proteins, and other signaling systems that interact with calcium pathway, like ion channels, pumps and exchangers, nitric oxide, glutamate, and others. The cascade of processes initiated by oxidative stress and ischemia in nervous tissue, includes both protective responses and apoptotic or necrotic cell death scenarios. This mini review surveys the publications on these processes and compares them with the data obtained in our laboratory on the model of photothrombotic stroke on rat brain in vivo and the model of photodynamic treatment on crayfish mechanoreceptor in vitro. These areas of research are driven by the need to find methods of emergency neuroprotection in ischemic stroke and to improve the accuracy and efficiency of photodynamic therapy of tumors with minimized damage to benign tissues. A proteomic study of the penumbra region in the photothrombotic stroke model revealed changes in the expression of a number of calcium-dependent proteins associated with impaired calcium homeostasis and having either a protective or damaging tendency. Inhibitory analysis of the effects of photo-oxidative stress on the crayfish stretch receptor model revealed the involvement of a number of proteins in the calcium-dependent pathway in neuronal or glial cell death or survival. In this paper, these data are analyzed and summarized to identify promising directions for further research.

Exosomes, the subclass of small membrane extracellular vesicles, have great diagnostic and therapeutic potential, but the lack of standardized methods for their efficient isolation and analysis limits the introduction of exosomal technologies into clinical practice. This review discusses the problems associated with the isolation of exosomes from biological fluids, as well as the principles of traditional and alternative methods of isolation. The aim of the presented review is to illustrate the variety of approaches based on the physical and biochemical properties of exosomes that can be used for exosome isolation. The advantages and disadvantages of different methods are discussed.

The role of various membrane components, phospholipids and lipopolysaccharides, in the formation and functioning of ion channels formed by lantibiotics of class A, nisin, and class B, cinnamycin and duramycin, was studied. Threshold concentrations of the tested lantibiotics were determined that cause ion channel formation and destruction of planar lipid bilayers. It was found that nisin was able to form ion channels with a conductance in the range from 2 to 600 pS at a concentration of more than 40 μM both in negatively charged lipid bilayers containing a specific adjuvant of gram-negative bacterial membranes, Kdo₂–lipid A, and in cardiolipin-containing membranes. The obtained results allowed suggesting that in model lipid membranes without lipid II, a precursor of peptidoglycan of gram-positive bacteria, which is a specific receptor of nisin, its role can be performed by Kdo₂–lipid A and cardiolipin. It was found that cinnamycin and its close analogue duramycin at concentrations of 1.5–3 μM induced step-like current fluctuations corresponding to the functioning of single ion channels with amplitudes from 5 to 30 pS and from 50 to 900 pS in membranes of phosphatidylethanolamine and cardiolipin-enriched bilayers, respectively. Based on the results obtained, we conclude that the channel-forming ability of cinnamycin and duramycin depends on the presence in the membrane of lipids prone to the formation of inverted hexagonal phases and the induction of spontaneous negative curvature in lipid monolayers.