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Applying TQRPA calculations of Gamow–Teller strength functions in hot nuclei, we compute the (anti)neutrino spectra and energy loss rates arising from weak processes on hot 56Fe under pre-supernova conditions. We use a realistic pre-supernova model calculated by the stellar evolution code MESA. Taking into account both charged and neutral current processes, we demonstrate that weak reactions with hot nuclei can produce high-energy (anti)neutrinos. We also show that, for hot nuclei, the energy loss via (anti)neutrino emission is significantly larger than that for nuclei in their ground state. It is found that the neutral current de-excitation via the νν¯-pair emission is presumably a dominant source of antineutrinos. In accordance with other studies, we confirm that the so-called single-state approximation for neutrino spectra might fail under certain pre-supernova conditions.

The animal cell is a unique system in which the functioning of its constituent molecules is interdependent and coordinated, and the violation of this coordination is fatal for the cell. One example of this coordination and mutual regulation is the functioning of membrane proteins, whose activity depends on their interaction with membrane lipids. This review reminds us of the crucial importance of the lipid component of cell membranes for normal cell function, and in particular looks at the role of the "cholesterol" component. Given a given genome and a corresponding set of proteins, this lipid component provides a wide range of regulation of cellular functions. The review exemplifies cholesterol-dependent membrane proteins and cellular processes and considers their role in microbial infections and some other pathologies. The concept of cholesterol-recognizing/interacting amino acid consensus (CRAC) motifs in proteins as a possible mechanism of these protein–lipid interactions is discussed. Examples of the use of peptides containing such motifs to modulate cholesterol-dependent processes are presented. In summary, consideration of the cholesterol component in disease pathogenesis and understanding the mechanisms of cholesterol–protein interactions represent a significant resource for the development of drugs that affect the protein–lipid interface. Such drugs may include cholesterol-binding peptides that target specific cholesterol-dependent proteins.

The activity of many membrane proteins, such as receptors, ionic channels, transporters, and enzymes, is cholesterol dependent; however, mechanisms of the cholesterol-dependent regulation of protein functions remain obscure. Recent studies suggest that membrane proteins can directly interact with cholesterol owing to the presence of the cholesterol-recognizing amino-acid consensus (CRAC) motifs. One of the ways to verify and further develop this notion is a design of CRAC-containing peptides and investigation of their effects on cholesterol-dependent cell functions. Previously we showed that a newly constructed peptide RTKLWEMLVELGNMDKAVKLWRKLKR (peptide P4) containing two CRAC motifs modulates cholesterol-dependent interactions of cultured macrophages IC-21 with 2-μm particles. In this work, in order to clarify the role of CRAC-forming amino acids, we employed the same experimental system to test the activity of peptides closely related to P4 but with modified CRAC motifs. We found that peptide STKLSEMLSELGNMDKASKLSRKLSR (Mut2) analogous to P4, except that all CRAC-forming amino acids (V, W, K/R) were substituted by serine, did not produce any effect in the concentration range 0.5-50 μM corresponding to the range of the P4 activity. Neither was effective peptide RTKLSEMLVELGNMDKAVKLSRKLKR (Mut3), in which only aromatic amino acids (W) of the CRAC motifs were substituted. Peptide STKLWEMLVELGNMDKAVKLWRKLSR (Mut4), in which only cationic amino acids (R/K) in the CRAC motifs were changed, produced almost the same effect as that of peptide P4 with a bell-shape dose-response curve. At low concentrations (1-4 μM) Mut4 notably increased the number of beads per cell, at higher concentrations this parameter diminished, and at 50 μM Mut4 produced a robust toxic effect. Finally, peptide EWGMAVLWERNRKLKKDLKVLKMLRT (Mut1) composed of the same amino acid residues as P4 but in a random order ("scramble") and possessing one CRAC motif, different from that in P4, produced a moderate stimulation at 4-10 μM but was not toxic at 50 μM. As in the case of peptide P4, the effects of Mut4 and Mut1 depended on the cholesterol content in the cell membrane: after the incubation of cells with cholesterol-extracting agent methyl-β-cyclodextrin stimulatory effects produced by Mut4 and Mut1 at low doses were suppressed. Our results indicate that CRAC motifs play an important role in the mechanisms of the peptide-induced modulations of cholesterol-dependent cell functions in the experimental system used and that of the three motif-forming amino acids, critical is the presence of the aromatic amino acid (W). Further research is required to comprehend the molecular mechanisms of interactions of CRAC-containing peptides with cell membrane components that lead to modulation of cell functions. We anticipate that CRAC-containing peptides may provide a basis for the development of new tools for directed regulation of the activity of target cholesterol-dependent membrane proteins and for the design of new antimicrobial and immunomodulating drugs in particular.

Some interactions of enveloped viruses with the host cell membrane have a cholesterol-dependent component, which may account for clinical manifestations of the infectious disease and can be used for the development of antiviral drugs. These cholesterol-dependent interactions can be mediated by cholesterol-recognition amino-acid consensus (CRAC) motifs present in viral proteins. The S protein of the SARS-CoV and SARS-CoV2 coronaviruses contains CRAC motifs that can be involved in the process of virus entry into the cell. Besides, during viral envelope formation, CRAC motifs can be responsible for binding of cell membrane cholesterol, leading to depletion of cell membrane cholesterol and subsequent malfunctioning of cellular cholesterol-dependent proteins, destabilization and permeabilization of cell membranes and, ultimately, to the death of infected cells. Understanding the mechanisms of cholesterol-dependent virus–cell interactions and the role of CRAC-containing viral proteins in the pathogenesis of the disease can serve as the basis for the development of new drugs that prevent both coronavirus entry into the cell and the damage of the infected cell during the viral morphogenesis. The target for such drugs can be the S-protein/cholesterol interface. CRAC-containing peptides derived from viral proteins may be among these agents. These peptides can also be used as experimental tools to study cholesterol-dependent virus–cell interactions.

Functioning of many membrane proteins is regulated by cholesterol. Some proteins were shown to contain cholesterol-recognizing amino-acid consensus (CRAC) motif. In particular, influenza virus protein M1 bears these motifs. To study functional roles and action mechanisms of peptides containing cholesterol-recognizing amino-acid consensus (CRAC) motifs, we designed and synthesized peptide RTKLWEMLVELGNMDKAVKLWRKLKR (peptide P4), which includes two peptides corresponding to CRAC-containing α-helices 3 and 6 of influenza virus protein M1 (LEVLMEWLKTR, aa 39–49, and NNMDKAVKLYRKLK, aa 91–105, respectively). We show that peptide P4 in a concentration range from 0.5 to 50 μM dose-dependently modulates cholesterol-dependent interactions of cultured macrophages IC-21 with 2-micron latex particles mimicking bacteria. The effect of peptide P4 was stronger than the effects of the composing peptides studied previously and exhibited a biphasic dose–response relationship. At concentrations from 0.5 to 10 μM peptide P4 significantly increased the number of cell-associated particles; at concentrations 10–20 μM the number of cell-associated particles decreased, and at concentrations 20–50 μM peptide P4 suppressed the cell activity and cell adhesion and produced a toxic effect. Upon extraction of membrane cholesterol by means of methyl-β-cyclodextrin the inhibitory effects of peptide P4 developed at much lower concentrations. The biphasic dose-dependence of the peptide P4 effect and the influence of methyl-β-cyclodextrin can be explained by the ability of peptide P4 to interact with membrane cholesterol. We suggest that peptide P4 at low concentrations facilitates the formation of cholesterol-enriched domains in plasma membrane and thus stimulates aggregation of cell receptors responsible for interactions of macrophages with particles. At higher concentrations peptide P4 may interfere with the activity of cholesterol-dependent receptors due to competitive binding of cholesterol and thus suppress both cell–particle and cell–substrate interactions. We believe that peptide P4 may serve as a useful tool for studies of cholesterol-dependent processes in cells and may serve a basis for the design of new antimicrobial and immunomodulating substances.

Entry of many viral and bacterial pathogens into host cells depends on cholesterol and/or cholesterol-enriched domains (lipid rafts) in the cell membrane. Earlier, we showed that influenza virus A matrix protein M1 contains amphipathic α-helices with exposed cholesterol-recognizing amino acid consensus (CRAC) motifs. In order to test possible functional activity of these motifs, we studied the effects of three synthetic peptides corresponding to the CRAC-containing α-helices of the viral M1 protein on the phagocytic activity of cultured mouse IC-21 macrophages. The following peptides were used: LEVLMEWLKTR (M1 α-helix 3, a.a. 39-49; further referred to as peptide 1), NNMDKAVKLYRKLK (M1 α-helix 6, a.a. 91-105; peptide 2), and GLKNDLLENLQAYQKR (M1 α-helix 13, a.a. 228-243; peptide 3). We found that all three peptides modulated interactions of IC-21 macrophages with non-opsonized 2-µm target particles. The greatest effect was demonstrated by peptide 2: in the presence of 35 μM peptide 2, the phagocytic index of IC-21 macrophages exceeded the control value by 60%; 10-11 mM methyl-β-cyclodextrin abolished this effect. Peptides 1 and 3 exerted weak inhibitory effect in a narrow concentration range of 5-10 μM. The dose-response curves could be approximated by a sum of two (stimulatory and inhibitory) components with different Hill coefficients, suggesting existence of at least two peptide-binding sites with different affinities on the cell surface. CD spectroscopy confirmed that the peptides exhibit structural flexibility in solutions. Altogether, our data indicate that amphipathic CRAC-containing peptides derived from the viral M1 protein modulate lipid raft-dependent processes in IC-21 macrophages.

It is known that the replacement of easily utilizable glucose with sorbitol in a medium activates a large number of repressed genes and metabolic changes in Neurospora crassa, which manifest themselves at the cellular level in a considerable vacuolization of the cytoplasm. The study of the morphological parameters and growth characteristics of isolated apical fragments of N. crassa hyphae showed that, in sorbitol-containing medium, the isolation from the parent mycelium causes the same disturbances in the coordination of elongation, branching, and septation as those described by us earlier for the glucose-containing medium. The metabolic changes caused by the carbon source replacement do not affect the hyphal-segment size, the distance from the growth point to the first septum, and the morphology and distribution of nuclei.

Some interactions of enveloped viruses with the host cell membrane have a cholesterol-dependent component, which may account for clinical manifestations of the infectious disease and can be used for the development of antiviral drugs. These cholesterol-dependent interactions can be mediated by cholesterol-recognition amino-acid consensus (CRAC) motifs present in viral proteins. The S protein of the SARS-CoV and SARS-CoV2 coronaviruses contains CRAC motifs that can be involved in the process of virus entry into the cell. Besides, during viral envelope formation, CRAC motifs can be responsible for binding of cell membrane cholesterol, leading to depletion of cell membrane cholesterol and subsequent malfunctioning of cellular cholesterol-dependent proteins, destabilization and permeabilization of cell membranes and, ultimately, to the death of infected cells. Understanding the mechanisms of cholesterol-dependent virus–cell interactions and the role of CRAC-containing viral proteins in the pathogenesis of the disease can serve as the basis for the development of new drugs that prevent both coronavirus entry into the cell and the damage of the infected cell during the viral morphogenesis. The target for such drugs can be the S-protein/cholesterol interface. CRAC-containing peptides derived from viral proteins may be among these agents. These peptides can also be used as experimental tools to study cholesterol-dependent virus–cell interactions.

Nebulette physically links desmin to sarcomeric actin in hearts. An intact desmin network is required for nebulette to function as major actin-binding protein in sarcomeres. This study provides biochemical evidence that the desmin–nebulette complex is involved in filament-forming desminopathy., In the hearts of patients bearing nebulette mutations, a severe general disorganization in cardiomyocytes of the extrasarcomeric desmin intermediate filament system is frequently observed. However, the molecular and functional relationship between the desmin cytoskeleton and nebulette-containing sarcomeres is still unclear. Here we report a high-affinity in vitro interaction between nebulette and desmin filaments. A major interaction site has been mapped to the desmin α-helical rod domain, indicating that the filament core is directly involved in the binding of nebulette. The disease-mutant desmin variants E245D and T453I exhibited increased binding affinity for nebulette, delayed filament assembly kinetics, and caused significant weakening of networks. In isolated chick cardiomyocytes and sections from canine heart, we revealed by ground-state depletion and confocal microscopies that module 5 of nebulette extends outward from Z-disk–associated desmin filaments toward the center of the sarcomere. Accordingly, in the myocardium of Des−/− mice, elevated levels of cardiac actin correlated with alterations in the distribution of nebulette. Our data suggest that a well-organized desmin network is required to accommodate an optimal conformation of nebulette on sarcomeres to bind and recruit cardiac α-actin. Hence we propose that nebulette acts in synergy with nebulin to reinforce and temporally fine-tune striated muscle relaxation–contraction cycles.

This corrects the article DOI: 10.1134/S0006297918080096.

With the aid of intracellular fluorescent probes, peculiarities of elongation, branching, septation, and nucleus morphology have been studied in isolated 400-μm-long apical fragments of Neurospora crassa hyphae growing for several hours without the influx of the nutrient materials from the mycelium. We found that: 1) the diameter and growth rate of newly developing branches decreased as compared to intact mycelium (from 10-20 to 6.5 ± 0.4 μm and from 24 ± 1 to 6.7 ± 0.5 μm/min, respectively), but the initial orientation of growth did not change; 2) the branching rhythm was altered; abnormally long internode distances appeared (up to 1471 μm), and the development of some side-branch buds ceased; 3) the character of the septation remained unchanged, as well as the hyphal segment length (68 ± 2 μm). In hyphae growing for 4.5-5.0 h in isolation from the whole mycelium, the distance between the tip and the first septum was 210 ± 15 μm, which was comparable with the respective value in intact mycelium, whereas the mean distance between the growth tip and the first side branch (492 ±127 μm) and the dispersion of this parameter was considerably higher than in intact mycelium. In branches growing in isolation from the intact mycelium for 1.5-4.5 h, the length of the nucleus- free apical zones near the growth tip (from 5 to 33 μm) and the nucleus morphology were similar to the respective characteristics known for the N. crassa mycelium. The experimental model described here can be used for the investigations of molecular and genetic mechanisms regulating the interactions between intracellular structures involved in the tip growth of N. crassa.

Beryllium has multiple industrial applications, but its manufacture is associated with a serious occupational risk of developing chronic inflammation in the lungs known as berylliosis, or chronic beryllium disease. Although the Be2+-induced abnormal immune responses have recently been linked to a specific MHC-II allele, the nature of long-lasting granulomas is not fully understood. Here we show that Be2+ binds with a micromolar affinity to phosphatidylserine (PS), the major surface marker of apoptotic cells. Isothermal titration calorimetry indicates that, like that of Ca2+, binding of Be2+ to PS liposomes is largely entropically driven, likely by massive desolvation. Be2+ exerts a compacting effect on PS monolayers, suggesting cross-linking through coordination by both phosphates and carboxyls in multiple configurations, which were visualized in molecular dynamics simulations. Electrostatic modification of PS membranes by Be2+ includes complete neutralization of surface charges at ∼30 μM, accompanied by ...