Capture and neutralization of SARS-CoV-2 and influenza virus by algae-derived lectins with high-mannose and core fucose specificities.

We first investigated the interactions between several algae-derived lectins and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). We created lectin columns using high-mannose (HM)-type glycan-specific lectins OAA and KAA-1 or core fucose-specific lectin hypninA-2 and conducted binding experiments with SARS-CoV-2. The results showed that these lectins were capable of binding to the virus. Furthermore, when examining the neutralization ability of nine different lectins, it was found that KAA-1, ESA-2, and hypninA-2 were effective in neutralizing SARS-CoV-2. In competitive inhibition experiments with glycoproteins, neutralization was confirmed to occur through HM-type or core fucose-type glycans. However, neutralization was not observed with other lectins, such as OAA. This trend of KAA-1 and ESA-2 having the neutralizing ability and OAA not having it was also similar to influenza viruses. Electron microscopy observations revealed that KAA-1 and hypninA-2 strongly aggregated SARS-CoV-2 particles, while OAA showed a low degree of aggregation. It is believed that the neutralization of SARS-CoV-2 involves multiple factors, such as glycan attachment sites on the S protein, the size of lectins, and their propensity to aggregate, which cause inhibition of receptor binding or aggregation of virus particles. This study demonstrated that several algae-derived lectins could neutralize SARS-CoV-2 and that lectin columns can effectively recover and concentrate the virus.

Structural basis of spike RBM-specific human antibodies counteracting broad SARS-CoV-2 variants.

The decrease of antibody efficacy to mutated SARS-CoV-2 spike RBD explains the breakthrough infections and reinfections by Omicron variants. Here, we analyzed broadly neutralizing antibodies isolated from long-term hospitalized convalescent patients of early SARS-CoV-2 strains. One of the antibodies named NCV2SG48 is highly potent to broad SARS-CoV-2 variants including Omicron BA.1, BA.2, and BA.4/5. To reveal the mode of action, we determined the sequence and crystal structure of the Fab fragment of NCV2SG48 in a complex with spike RBD from the original, Delta, and Omicron BA.1. NCV2SG48 is from a minor VH but the multiple somatic hypermutations contribute to a markedly extended binding interface and hydrogen bonds to interact with conserved residues at the core receptor-binding motif of RBD, which efficiently neutralizes a broad spectrum of variants. Thus, eliciting the RBD-specific B cells to the longitudinal germinal center reaction confers potent immunity to broad SARS-CoV-2 variants emerging one after another.

Vaccination with the Omicron spike RBD boosts broadly neutralizing antibody levels and confers sustained protection even after acquiring immunity to the original antigen.

The immune evasion of SARS-CoV-2 Omicron variants caused by multiple amino acid replacements in the receptor-binding domain (RBD) of spike protein wanes the effectiveness of antibodies elicited by current SARS-CoV-2 booster vaccination. The vaccines that target Omicron strains have been recently developed, however, there has been a concern yet to be addressed regarding the negative aspect of the immune response known as original antigenic sin. Here we demonstrate that the breadth of neutralizing antibodies against SARS-CoV-2 variants is barely elicited by immunizing monovalent viral antigens via vaccination or natural infection in mice and human subjects. However, vaccination of Omicron BA.1 RBD to pre-immunized mice with the original RBD conferred sustained neutralizing activity to BA.1 and BA.2 not only original pseudoviruses. The acquisition of neutralizing antibody breadth was further confirmed in vaccinated-then-Omicron convalescent human sera in which neutralizing activity against BA.1 and BA.2 pseudoviruses was highly induced. Thus, our data suggest that Omicron-specific vaccines or the infection with Omicron viruses can boost potent neutralizing antibodies to the Omicron variants even in the host pre-vaccinated with the original antigen.

Thermal Structure Transformation of Methylammonium Vanadate and it's Application as a Negative Staining Reagent for Observing SARS‐CoV‐2

The solid‐state thermal structure transformation of methylammonium vanadate, (CH3NH3)VO3, from −150 °C to 350 °C is reported. Variable‐temperature X‐ray single‐crystal structure analysis at 23, 0, −50, −100, and −150 °C reveal (CH3NH3)VO3 comprises of methylammonium cations and “snake‐like” ([VO3]−)n anion chains propagating along the c‐direction in the Pna21 space group. In between −150 and −100 °C, we observe a reversible structural transformation due to the re‐orientation of the methylammonium cations in the crystal packing, which is also confirmed by the reversible profiles observed in differential scanning calorimetry. The methylammonium vanadate is stable until at ca. 100 °C and further heating releases methylamine and water and V2O5 is formed at ca. 275 °C . Furthermore, we show that the methylammonium vanadate can be used as a negative staining reagent for visualizing SARS‐CoV‐2, allowing us to discern the spike proteins from the body of the virus using transmission electron microscopy. Methylammonium vanadate, [(CH3NH3)VO3]n, shows a reversible structure transformation due to change of methylammonium cation orientation between −100 and −150 °C. In contrast, heating causes decomposition to form V2O5. The methylammonium vanadate can be used as a negative staining reagent for visualizing SARS‐CoV‐2 using transmission electron microscopy.

Thermal Structure Transformation of Methylammonium Vanadate and it's Application as a Negative Staining Reagent for Observing SARS-CoV-2.

The solid-state thermal structure transformation of methylammonium vanadate, (CH3NH3)VO3, from -150 °C to 350 °C is reported. Variable-temperature X-ray single-crystal structure analysis at 23, 0, -50, -100, and -150 °C reveal (CH3NH3)VO3 comprises of methylammonium cations and "snake-like" ([VO3]-)n anion chains propagating along the c-direction in the Pna21 space group. In between -150 and -100 °C, we observe a reversible structural transformation due to the re-orientation of the methylammonium cations in the crystal packing, which is also confirmed by the reversible profiles observed in differential scanning calorimetry. The methylammonium vanadate is stable until at ca. 100 °C and further heating releases methylamine and water and V2O5 is formed at ca. 275 °C . Furthermore, we show that the methylammonium vanadate can be used as a negative staining reagent for visualizing SARS-CoV-2, allowing us to discern the spike proteins from the body of the virus using transmission electron microscopy.

Ethanol Susceptibility of SARS-CoV-2 and Other Enveloped Viruses.

Ethanol is an effective disinfectant against the novel coronavirus SARS-CoV-2. However, its effective concentration has not been shown, and we therefore analyzed the effects of different concentrations of ethanol on SARS-CoV-2. When SARS-CoV-2 was treated with varying ethanol concentrations and examined for changes in infectivity, the ethanol concentration at which 99% of the infectious titers were reduced was 24.1% (w/w) [29.3% (v/v)]. For reference, ethanol susceptibility was also examined with other envelope viruses, including influenza virus, vesicular stomatitis virus in the family Rhabdoviridae, and Newcastle disease virus in the family Paramyxoviridae, and the 99% inhibitory concentrations were found to be 28.8%(w/w) [34.8% (v/v)], 24.0% (w/w) [29.2% (v/v)], and 13.3% (w/w) [16.4% (v/v)], respectively. Some differences from SARS-CoV-2 were observed, but the differences were not significant. It was concluded that ethanol at a concentration of 30%(w/w) [36.2% (v/v)] almost completely inactivates SARS-CoV-2.