Anti-stokes fluorescence of phycobilisome and its complex with the orange carotenoid protein.

Phycobilisomes (PBSs) are giant water-soluble light-harvesting complexes of cyanobacteria and red algae, consisting of hundreds of phycobiliproteins precisely organized to deliver the energy of absorbed light to chlorophyll chromophores of the photosynthetic electron-transport chain. Quenching the excess of excitation energy is necessary for the photoprotection of photosynthetic apparatus. In cyanobacteria, quenching of PBS excitation is provided by the Orange Carotenoid Protein (OCP), which is activated under high light conditions. In this work, we describe parameters of anti-Stokes fluorescence of cyanobacterial PBSs in quenched and unquenched states. We compare the fluorescence readout from entire phycobilisomes and their fragments. The obtained results revealed the heterogeneity of conformations of chromophores in isolated phycobiliproteins, while such heterogeneity was not observed in the entire PBS. Under excitation by low-energy quanta, we did not detect a significant uphill energy transfer from the core to the peripheral rods of PBS, while the one from the terminal emitters to the bulk allophycocyanin chromophores is highly probable. We show that this direction of energy migration does not eliminate fluorescence quenching in the complex with OCP. Thus, long-wave excitation provides new insights into the pathways of energy conversion in the phycobilisome.

Visualization of electric fields and associated behavior in fish and other aquatic animals.

In some fish lineages, evolution has led to unique sensory adaptations that provide information which is not available to terrestrial animals. These sensory systems include, among others, electroreception, which together with the ability of fish to generate electric discharges plays a role in social communication and object location. Most studies on electric phenomena in aquatic animals are dedicated to selected groups of electric fishes that regularly generate electric signals (Mormyriformes, Gymnotiformes). There exist, however, several species (hitherto described as non-electric) which, though able to perceive electric signals, have now been found to also generate them. In this article, we introduce a tool that we have designed to investigate such electric activity. This required significant adaptations of the equipment used in fish with regular discharge generation. The necessary improvements were realized by using a multielectrode registration setup allowing simultaneous visualization and quantification of behavior and associated electric activity of fish, alone or in groups, with combined electro-video clips. Precise synchronization of locomotor and electric behaviors made it possible to determine the electrically active fish in a group, and also the location of the electrogenic structure inside the fish's body. Our simple registration procedure, together with data presentation, should attract a broad audience of scientists taking up the challenge of uncovering electric phenomena in aquatic animals currently treated as electrically inactive.

Triggering gel-sol transition by weak magnetic field.

The self-assembly of small and always chiral molecules into fiber-like structures is a mysterious process, as the physics underlying such self-assembly is unclear. The energy necessary for this process exceeds the one provided by common dispersion interactions and hydrogen bonding. The recent results obtained by the scientific group of Prof. Naaman from the Weizmann Institute of Science fed light on the nature of forces providing for the self-assembly of chiral molecules and attributed these forces to spin-exchange interactions. Therefore, the self-assembly of chiral molecules should be magneto-sensitive. We found such sensitivity in solutions of trifluoroacetylated α -amino alcohols, and the process was inhibited by the magnetic field when fibers grew on the surface of the substrate. On the contrary, in bulk, the self-assembly was enhanced by the magnetic field and led to the formation of a dense gel, while no gelation was observed in the absence of the external magnetic field. The latter observations are the theme of this short report, aimed to declare the effect itself but not pretend to describe it in full.

Anti-cancer activity of ultra-short single-stranded polydeoxyribonucleotides.

One of the features that differentiate cancer cells is their increased proliferation rate, which creates an opportunity for general anti-tumor therapy directed against the elevated activity of replicative apparatus in tumor cells. Besides DNA synthesis, successful genome replication requires the reparation of the newly synthesized DNA. Malfunctions in reparation can cause fatal injuries in the genome and cell death. Recently we have found that the ultra-short single-stranded deoxyribose polynucleotides of random sequence (ssDNA) effectively inhibit the catalytic activity of DNA polymerase [Formula: see text]. This effect allowed considering these substances as potential anti-tumor drugs, which was confirmed experimentally both in vitro (using cancer cell cultures) and in vivo (using cancer models in mice). According to the obtained results, ssDNA significantly suppresses cancer development and tumor growth, allowing consideration of them as novel candidates for anti-cancer drugs.

Magnetic field and nuclear spin influence on the DNA synthesis rate.

The rate of a chemical reaction can be sensitive to the isotope composition of the reactants, which provides also for the sensitivity of such "spin-sensitive" reactions to the external magnetic field. Here we demonstrate the effect of the external magnetic field on the enzymatic DNA synthesis together with the effect of the spin-bearing magnesium ions ([Formula: see text]Mg). The rate of DNA synthesis monotonously decreased with the external magnetic field induction increasing in presence of zero-spin magnesium ions ([Formula: see text]Mg). On the contrary, in the presence of the spin-bearing magnesium ions, the dependence of the reaction rate on the magnetic field induction was non-monotonous and possess a distinct minimum at 80-100 mT. To describe the observed effect, we suggested a chemical scheme and biophysical mechanism considering a competition between Zeeman and Fermi interactions in the external magnetic field.

The role of the local environment on the structural heterogeneity of carotenoid ß-ionone rings.

Our analysis of the X-ray crystal structure of canthaxanthin (CAN) showed that its ketolated ß-ionone rings can adopt two energetically equal, but structurally distinct puckers. Quantum chemistry calculations revealed that the potential energy surface of the ß-ionone ring rotation over the plane of the conjugated π-system in carotenoids depends on the pucker state of the ß-ring. Considering different pucker states and ß-ionone ring rotation, we found six separate local minima on the potential energy surface defining the geometry of the keto-ß-ionone ring-two cis and one trans orientation for each of two pucker states. We observed a small difference in energy and no difference in relative orientation for the cis-minima, but a pronounced difference for the position of trans-minimum in alternative pucker configurations. An energetic advantage of ß-ionone ring rotation from a specific pucker type can reach up to 8 kJ/mol ([Formula: see text]). In addition, we performed the simulation of linear absorption of CAN in hexane and in a unit cell of the CAN crystal. The electronic energies of [Formula: see text] transition were estimated both for the CAN monomer and in the CAN crystal. The difference between them reached [Formula: see text], which roughly corresponds to the energy gap between A and B pucker states predicted by theoretical estimations. Finally, we have discussed the importance of such effects for biological systems whose local environment determines conformational mobility, and optical/functional characteristics of carotenoid.

Probing Red Blood Cell Membrane Microviscosity Using Fluorescence Anisotropy Decay Curves of the Lipophilic Dye PKH26.

Red blood cell (RBC) aggregation and deformation are governed by the molecular processes occurring on the membrane. Since several social important diseases are accompanied by alterations in RBC aggregation and deformability, it is important to develop a diagnostic parameter of RBC membrane structural integrity and stability. In this work, we propose membrane microviscosity assessed by time-resolved fluorescence anisotropy of the lipophilic PKH26 fluorescent probe as a diagnostic parameter. We measured the fluorescence decay curves of the PKH26 probe in the RBC membrane to establish the optimal parameters of the developed fluorescence assay. We observed a complex biphasic profile of the fluorescence anisotropy decay characterized by two correlation times corresponding to the rotational diffusion of free PKH26, and membrane-bounded molecules of the probe. The developed assay allowed us to estimate membrane microviscosity ηm in the range of 100-500 cP depending on the temperature, which paves the way for assessing RBC membrane properties in clinical applications as predictors of blood microrheological abnormalities.

Modulation of Membrane Microviscosity by Protein-Mediated Carotenoid Delivery as Revealed by Time-Resolved Fluorescence Anisotropy.

Carotenoids are potent antioxidants with a wide range of biomedical applications. However, their delivery into human cells is challenging and relatively inefficient. While the use of natural water-soluble carotenoproteins capable to reversibly bind carotenoids and transfer them into membranes is promising, the quantitative estimation of the delivery remains unclear. In the present work, we studied echinenone (ECN) delivery by cyanobacterial carotenoprotein AnaCTDH (C-terminal domain homolog of the Orange Carotenoid Protein from Anabaena), into liposome membranes labelled with BODIPY fluorescent probe. We observed that addition of AnaCTDH-ECN to liposomes led to the significant changes in the fast-kinetic component of the fluorescence decay curve, pointing on the dipole-dipole interactions between the probe and ECN within the membrane. It may serve as an indirect evidence of ECN delivery into membrane. To study the delivery in detail, we carried out molecular dynamics modeling of the localization of ECN within the lipid bilayer and calculate its orientation factor. Next, we exploited FRET to assess concentration of ECN delivered by AnaCTDH. Finally, we used time-resolved fluorescence anisotropy to assess changes in microviscosity of liposomal membranes. Incorporation of liposomes with ß-carotene increased membrane microviscosity while the effect of astaxanthin and its mono- and diester forms was less pronounced. At temperatures below 30 °C addition of AnaCTDH-ECN increased membrane microviscosity in a concentration-dependent manner, supporting the protein-mediated carotenoid delivery mechanism. Combining all data, we propose FRET-based analysis and assessment of membrane microviscosity as potent approaches to characterize the efficiency of carotenoids delivery into membranes.

The role of exchange interactions in the stability of cellulose.

The problem of the origin of biochirality and the related problem of the initial monomer selection are still under discussion, and the main point here is not the mechanics of enantiomer separation but the problem of the role of chirality in the very early stages of evolution. A recent breakthrough in understanding the influence of a static magnetic field on non-magnetic systems can shed light on this complex problem. The phenomenon of magnetosensitivity of non-magnetic systems was reported for only chiral systems and was closely related to the ability of some chiral substances to self-assemble. We suppose the chirality was essential due to the quantum spin-related effects arising between the interacting chiral molecules and providing for the self-assembly phenomenon. Here we demonstrate the magnetosensitivity of the supramolecular packing of cellulose chains, directly indicating the reliability of the supposition above.

A gel lattice alters the phase state of a solvent.

Some low-molecular-weight substances are able to self-assemble into fiber-like structures (strings) to form gels. One of the examples of such substances is trifluoroacetylated alpha-aminoalcohols (TFAAAs) able to gelate in many organic solvents. Here we report the formation and describe the properties of a layer of an altered solvent covering the strings' surface. The altered solvent layer has a different refractive index and melts at a temperature about several degrees lower than that of the bulk solvent. Moreover, the bulk solvent's melting temperature was also decreased by values far beyond the one expected according to Raoult's law. Based on the Gibbs-Thomson equation it is possible to derive the thickness of the special layer as well as the average gel lattice parameters, which were very stable across the variety of systems investigated.

Molecular Self-Assembly as a Trigger of Life Origin and Development.

The origin and reason for the homochirality of living cells go with the problem of a relatively narrow spectrum of the actual biological monomers compared to the whole theoretically possible spectrum of amino acids or carbohydrates. A limited number of bio-monomers implies some special feature differing from all other similar molecules that are not present in the living cell. Here we propose one of the candidates for such a peculiarity: the ability to form highly elongated helical supramolecular structures (strings) when precipitating from homochiral solutions. The strings' forming can be accompanied by spontaneous splitting and/or chiral purification of the initially racemic mixture. Our previous theoretical reasoning was based mainly on the biomimetic systems, while now we describe the strings forming in homochiral amino acid solutions.

Local Accumulation of Lymphocytes in the Intima of Human Aorta Is Associated with Giant Multinucleated Endothelial Cells: Possible Explanation for Mosaicism of Atherosclerosis.

Distribution of different types of atherosclerotic lesions in the arterial wall is not diffuse, but is characterized by mosaicism. The causes of such distribution remain to be established. At the early stages of atherogenesis, low-density lipoprotein (LDL) particles and immune cells penetrate into the intimal layer of the arterial wall through the endothelium. In adult humans, the luminal surface of the arterial wall is a heterogeneous monolayer of cells with varying morphology including typical endothelial cells (ECs) and multinucleated variant endothelial cells (MVECs). We hypothesized that distribution of MVECs in the endothelial monolayer can be related to the distribution pattern of early atherosclerotic lesions. We obtained en face preparations of intact adult (22-59 years old) aortic wall sections that allowed us to study the endothelial monolayer and the subendothelial layer. We compared the distribution of MVECs in the endothelial monolayer with the localization of early atherosclerotic lesions in the subendothelial layer, which were characterized by lipid accumulation and immune cell recruitment. In primary culture, MVECs demonstrated increased phagocytic activity compared to mononuclear ECs. Moreover, we have shown that unaffected aortic intima contained associates formed as a result of aggregation and/or fusion of LDL particles that are non-randomly distributed. This indicated that MVECs may be involved in the accumulation of LDL in the subendothelial layer through increased transcytosis. Interaction of LDL with subendothelial cells of human aorta in primary culture increased their adhesive properties toward circulating immune cells. Study of unaffected aortic intima revealed non-random distribution of leukocytes in the subendothelial layer and increased localization of CD45+ leukocytes in the subendothelial layer adjacent to MVECs. Together, our observations indicate that MVECs may be responsible for the distribution of atherosclerotic lesions in the arterial wall by participating in LDL internalization and immune cell recruitment.

State of the phycobilisome determines effective absorption cross-section of Photosystem II in Synechocystis sp. PCC 6803.

Quenching of excess excitation energy is necessary for the photoprotection of light-harvesting complexes. In cyanobacteria, quenching of phycobilisome (PBS) excitation energy is induced by the Orange Carotenoid Protein (OCP), which becomes photoactivated under high light conditions. A decrease in energy transfer efficiency from the PBSs to the reaction centers decreases photosystem II (PS II) activity. However, quantitative analysis of OCP-induced photoprotection in vivo is complicated by similar effects of both photochemical and non-photochemical quenching on the quantum yield of the PBS fluorescence overlapping with the emission of chlorophyll. In the present study, we have analyzed chlorophyll a fluorescence induction to estimate the effective cross-section of PS II and compared the effects of reversible OCP-dependent quenching of PBS fluorescence with reduction of PBS content upon nitrogen starvation or mutations of key PBS components. This approach allowed us to estimate the dependency of the rate constant of PS II primary electron acceptor reduction on the amount of PBSs in the cell. We found that OCP-dependent quenching triggered by blue light affects approximately half of PBSs coupled to PS II, indicating that under normal conditions, the concentration of OCP is not sufficient for quenching of all PBSs coupled to PS II.

Role of hydrogen bond alternation and charge transfer states in photoactivation of the Orange Carotenoid Protein.

Here, we propose a possible photoactivation mechanism of a 35-kDa blue light-triggered photoreceptor, the Orange Carotenoid Protein (OCP), suggesting that the reaction involves the transient formation of a protonated ketocarotenoid (oxocarbenium cation) state. Taking advantage of engineering an OCP variant carrying the Y201W mutation, which shows superior spectroscopic and structural properties, it is shown that the presence of Trp201 augments the impact of one critical H-bond between the ketocarotenoid and the protein. This confers an unprecedented homogeneity of the dark-adapted OCP state and substantially increases the yield of the excited photoproduct S*, which is important for the productive photocycle to proceed. A 1.37 Å crystal structure of OCP Y201W combined with femtosecond time-resolved absorption spectroscopy, kinetic analysis, and deconvolution of the spectral intermediates, as well as extensive quantum chemical calculations incorporating the effect of the local electric field, highlighted the role of charge-transfer states during OCP photoconversion.

On the orientation of the chains in the mercerized cellulose.

The cold alkaline treatment or mercerization of cellulose is widely used in industry to enrich the cellulose raw with high-molecular-weight [Formula: see text]-cellulose. Washing out of hemicelluloses by alkalies is accompanied by the rearrangement of the cellulose chains' packing, well known as a transition between cellulose I and cellulose II. Cellulose II can also be produced by the precipitation of the cellulose solutions (regeneration). The currently accepted theory implies that in cellulose II, both mercerized and regenerated, the macromolecules are arranged antiparallelly. However, forming such a structure in the course of the mercerization seems to be significantly hindered, while it seems to be quite possible in the regeneration process. In this work, we discuss the sticking points in the theory on the antiparallel structure of mercerized cellulose from a theoretical point of view summarizing all of the available experimental data in the field.

Antiviral potential of plant polysaccharide nanoparticles actuating non-specific immunity.

The development of high-end targeted drugs and vaccines against modern pandemic infections, such as COVID-19, can take a too long time that lets the epidemic spin up and harms society. However, the countermeasures must be applied against the infection in this period until the targeted drugs became available. In this regard, the non-specific, broad-spectrum anti-viral means could be considered as a compromise allowing overcoming the period of trial. One way to enhance the ability to resist the infection is to activate the nonspecific immunity using a suitable driving-up agent, such as plant polysaccharides, particularly our drug Panavir isolated from the potato shoots. Earlier, we have shown the noticeable anti-viral and anti-bacterial activity of Panavir. Here we demonstrate the pro-inflammation activity of Panavir, which four-to-eight times intensified the ATP and MIF secretion by HL-60 cells. This effect was mediated by the active phagocytosis of the Panavir particles by the cells. We hypothesized the physiological basis of the Panavir proinflammatory activity is mediated by the indol-containing compounds (auxins) present in Panavir and acting as a plant analog of serotonin.

Zhurkov's Stress-Driven Fracture as a Driving Force of the Microcrystalline Cellulose Formation.

Microcrystalline cellulose (MCC) is a chemically pure product of cellulose mechano-chemical conversion. It is a white powder composed of the short fragments of the plant cells widely used in the modern food industry and pharmaceutics. The acid hydrolysis of the bleached lignin-free cellulose raw is the main and necessary stage of MCC production. For this reason, the acid hydrolysis is generally accepted to be the driving force of the fragmentation of the initial cellulose fibers into MCC particles. However, the low sensibility of the MCC properties to repeating the hydrolysis forces doubting this point of view. The sharp, cleave-looking edges of the MCC particles suggesting the initial cellulose fibers were fractured; hence the hydrolysis made them brittle. Zhurkov showed that mechanical stress decreases the activation energy of the polymer fracture, which correlates with the elevated enthalpy of the MCC thermal destruction compared to the initial cellulose.

The weak magnetic field inhibits the supramolecular self-ordering of chiral molecules.

The magnetic field can affect processes in the non-magnetic systems, including the biochemical reactions in the living cells. This phenomenon becomes possible due to the fermionic nature of an electron and significant energy gain provided by the exchange interactions. Here we report the inhibition effect of the magnetic field on the processes of the chiral supramolecular, i.e., macroscopic self-ordering in the non-magnetic model system. The observed effect is in tune with the reports on the influence of the magnetic field on the adsorption of the chiral molecules, which was explained by the effect of the chirally-induced spin-selectivity and the inhibition of the chemical reactions caused by the singlet-triplet conversion. The magneto sensitivity of the process of the chiral self-ordering directly indicates its spin-polarization nature. Tacking together all of the results in the field, we can propose that the chirality-driven exchange interactions guide the selection of the chiral molecules and explain their prevalence in the living matter. It is also probable that these forces have played a critical role in the origin of life on Earth.

Antiviral activity of the high-molecular-weight plant polysaccharides (Panavir®).

This short report is dedicated to the description of the wide antiviral and antibacterial activity of the immune-modulating agent Panavir®. Panavir® is a high-molecular-weight fraction of the polysaccharides extracted from the shoots of the Solanum tuberosum. It demonstrates activity against many types of viruses, including animal coronavirus and also against bacterial infections. These properties look very promising considering the COVID-19 epidemy and allow propose that Panavir® would be effective in the therapy of the SARS-CoV-2 infection.