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— SARS-CoV-2, the causative agent of COVID-19, remains the focus of research worldwide. SARS-CoV-2 entry into the cell starts with its S protein binding to the angiotensin-converting enzyme-2 (ACE2) expressed on the cell surface. The knowledge of the S protein’s spatial structure is indispensable for understanding the molecular principles of its work. The S protein structure has been almost fully described using experimental approaches with the only exception for the protein’s endodomain, the transmembrane domain, and the ectodomain parts adjacent to the latter. The paper reports molecular modelling of the S protein fragment corresponding to its coiled coil HR2 domain and fully palmitoylated transmembrane domain. Model stability in lipid bilayer was confirmed by all-atom and coarse-grained molecular dynamics simulations. It has been demonstrated that palmitoylation leads to a significant decrease in transmembrane domain mobility and local bilayer thickening, which may be relevant for protein trimerization.

The severe COVID‐19 pandemic drives the research toward the SARS‐CoV‐2 virion structure and the possible therapies against it. Here, we characterized the β‐propiolactone inactivated SARS‐CoV‐2 virions using transmission electron microscopy (TEM) and atomic force microscopy (AFM). We compared the SARS‐CoV‐2 samples purified by two consecutive chromatographic procedures (size exclusion chromatography [SEC], followed by ion‐exchange chromatography [IEC]) with samples purified by ultracentrifugation. The samples prepared using SEC and IEC retained more spikes on the surface than the ones prepared using ultracentrifugation, as confirmed by TEM and AFM. TEM showed that the spike (S) proteins were in the pre‐fusion conformation. Notably, the S proteins could be recognized by specific monoclonal antibodies. Analytical TEM showed that the inactivated virions retained nucleic acid. Altogether, we demonstrated that the inactivated SARS‐CoV‐2 virions retain the structural features of native viruses and provide a prospective vaccine candidate., SARS‐CoV‐2 virions inactivated with β‐propiolactone were analyzed using transmission electron microscopy (TEM) and atomic force microscopy.The S proteins could be recognized by specific monoclonal antibodies.Analytical TEM showed that the inactivated virions retained nucleic acid.

Carotenoids astaxanthin and β-carotene are widely used natural antioxidants. They are key components of functional food, cosmetics, drugs and animal feeding. They hold leader positions on the world carotenoid market. In current work, we characterize the new strain of the green microalga Bracteacoccus aggregatus BM5/15 and propose the method of its culturing in a bubble-column photobioreactor for simultaneous production of astaxanthin and β-carotene. Culture was monitored by light microscopy and pigment kinetics. Fatty acid profile was evaluated by tandem gas-chromatography–mass spectrometry. Pigments were obtained by the classical two-stage scheme of autotrophic cultivation. At the first, vegetative, stage biomass accumulation occurred. Maximum specific growth rate and culture productivity at this stage were 100–200 mg∙L−1∙day−1, and 0.33 day−1, respectively. At the second, inductive, stage carotenoid synthesis was promoted. Maximal carotenoid fraction in the biomass was 2.2–2.4%. Based on chromatography data, astaxanthin and β-carotene constituted 48 and 13% of total carotenoid mass, respectively. Possible pathways of astaxanthin synthesis are proposed based on carotenoid composition. Collectively, a new strain B. aggregatus BM5/15 is a potential biotechnological source of two natural antioxidants, astaxanthin and β-carotene. The results give the rise for further works on optimization of B. aggregatus cultivation on an industrial scale.

Carotenogenic microalgae are unicellular photosynthetic organisms with the ability to accumulate carotenoids. Carotenoid accumulation is a protective reaction against environmental stress factors, such as bright light, extreme temperatures, etc. It makes the survival of these microorganisms under harsh environmental conditions possible. The diversity of carotenogenic microalgae has been described in detail for Central Europe and North America, as well as for tropical and subtropical latitudes with relatively favorable environmes. However, data about these microorganisms in polar and subpolar latitudes is scarce and restricted to few reports. We isolated several strains of carotenogenic microalgae from the coastal zone of the White Sea, where they were abundant. The obtained microalgae related to four species of Chlorophytes: Haematococcus lacustris, H. rubicundus, Coelastrella aeroterrestrica, and Bracteacoccus aggregatus. The last three species have been reported for polar latitudes for the first time. Most likely, carotenogenic algae in the White Sea coast are abundant due to their high physiological and metabolic plasticity, which is essential for surviving under adverse conditions of the northern regions. Pigment composition of the strains is provided. Their predominant carotenoids were astaxanthin and β-carotene. Further, the obtained strains may be considered as potential producers of natural pigments for biotechnology.

Background: The spike glycoprotein of SARS-coronavirus mediates the early events leading to infection of cells, including fusion of the viral and cellular membranes. The spike is a type I membrane glycoprotein that possesses a conserved transmembrane anchor and an unusual cysteine-rich domain that bridges the putative junction of the anchor and the cytoplasmic tail. In this study, we examined the role of these carboxyl-terminal domains in S-protein interaction with membrane. Methods: Structural model of the trimeric TM domain and adjacent fragments of ecto- and endo domains (residues 1157-1256) of the S-protein was built by homology basing on the solution structure of the SARS-coronavirus S-protein HR2 domain (pdb-code 2fxp), the structure of the transmembrane domain of HIV-1 gp41 in bicelle (5jyn), and assumption of generally coiled-coil fold of the considered domain. C-terminus of the domain was left unstructured but fully palmitoylated. Molecular dynamics simulation in heterogeneous lipid bilayer was prepared with CHARMM-GUI and performed with Gromacs during 100 ns. Results: 1. Ectodomain fragment (residues 1157-1212) demonstrates a tilt by the angle of 40-60 degrees from the axis of the TM domain (residues 1213-1237). This tilt is facilitated by glycine residues in position 1204. 2. Cholesterol molecules of the bottom layer tend to localize around protein due to interaction with palmitoyl tails while lipids in the upper layer do not show such tendency. Conclusion: Performed molecular simulations show that both palmitoylation and a large cluster of aromatic residues provide high stability of the S-protein TM domain.