ABSTRACT
Entry of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) into host cells depends on refolding of the virus-encoded spike protein from a prefusion conformation, metastable after cleavage, to a lower energy, stable postfusion conformation. This transition overcomes kinetic barriers for fusion of viral and target cell membranes. We report here a cryo-EM structure of the intact postfusion spike in a lipid bilayer that represents single-membrane product of the fusion reaction. The structure provides structural definition of the functionally critical membraneinteracting segments, including the fusion peptide and transmembrane anchor. The internal fusion peptide forms a hairpin-like wedge that spans almost the entire lipid bilayer and the transmembrane segment wraps around the fusion peptide at the last stage of membrane fusion. These results advance our understanding of the spike protein in a membrane environment and may guide development of intervention strategies.
ABSTRACT
The Omicron subvariant BA.2 has become the dominant circulating strain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in many countries. We have characterized structural, functional and antigenic properties of the full-length BA.2 spike (S) protein and compared replication of the authentic virus in cell culture and animal model with previously prevalent variants. BA.2 S can fuse membranes more efficiently than Omicron BA.1, mainly due to lack of a BA.1-specific mutation that may retard the receptor engagement, but still less efficiently than other variants. Both BA.1 and BA.2 viruses replicated substantially faster in animal lungs than the early G614 (B.1) strain in the absence of pre-existing immunity, possibly explaining the increased transmissibility despite their functionally compromised spikes. As in BA.1, mutations in the BA.2 S remodel its antigenic surfaces leading to strong resistance to neutralizing antibodies. These results suggest that both immune evasion and replicative advantage may contribute to the heightened transmissibility for the Omicron subvariants.
ABSTRACT
Individuals infected with the SARS-CoV-2 Delta variant, lineage B.1.617.2, exhibit faster initial infection with a higher viral load than prior variants, and pseudotyped particles bearing the SARS-CoV-2 Delta variant spike protein induce a faster initial infection rate of target cells compared to those bearing other SARS-CoV-2 variant spikes. Here, we show that pseudotyped particles bearing the Delta variant spike form unique aggregates, as evidenced by negative stain and cryogenic electron microscopy (EM), flow cytometry, and nanoparticle tracking analysis. Viral particles pseudotyped with other SARS-CoV-2 spike variants do not show aggregation by any of these criteria. The contribution to infection kinetics of the Delta spikes unique property to aggregate is discussed with respect to recent evidence for collective infection by other viruses. Irrespective of this intriguing possibility, spike-dependent aggregation is a new functional parameter of spike-expressing viral particles to evaluate in future spike protein variants.
ABSTRACT
The Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), bearing an unusually high number of mutations, has become a dominant strain in many countries within several weeks. We report here structural, functional and antigenic properties of its full-length spike (S) protein with a native sequence in comparison with those of previously prevalent variants. Omicron S requires a substantially higher level of host receptor ACE2 for efficient membrane fusion than other variants, possibly explaining its unexpected cellular tropism. Mutations not only remodel the antigenic structure of the N-terminal domain of the S protein, but also alter the surface of the receptor-binding domain in a way not seen in other variants, consistent with its remarkable resistance to neutralizing antibodies. These results suggest that Omicron S has acquired an extraordinary ability to evade host immunity by excessive mutations, which also compromise its fusogenic capability.
ABSTRACT
The Delta variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has outcompeted previously prevalent variants and become a dominant strain worldwide. We report here structure, function and antigenicity of its full-length spike (S) trimer in comparison with those of other variants, including Gamma, Kappa, and previously characterized Alpha and Beta. Delta S can fuse membranes more efficiently at low levels of cellular receptor ACE2 and its pseudotyped viruses infect target cells substantially faster than all other variants tested, possibly accounting for its heightened transmissibility. Mutations of each variant rearrange the antigenic surface of the N-terminal domain of the S protein in a unique way, but only cause local changes in the receptor-binding domain, consistent with greater resistance particular to neutralizing antibodies. These results advance our molecular understanding of distinct properties of these viruses and may guide intervention strategies.
ABSTRACT
Several fast-spreading variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have become the dominant circulating strains that continue to fuel the COVID-19 pandemic despite intensive vaccination efforts throughout the world. We report here cryo-EM structures of the full-length spike (S) trimers of the B.1.1.7 and B.1.351 variants, as well as their biochemical and antigenic properties. Mutations in the B.1.1.7 protein increase the accessibility of its receptor binding domain and also the binding affinity for receptor angiotensin-converting enzyme 2 (ACE2). The enhanced receptor engagement can account for the increased transmissibility and risk of mortality as the variant may begin to infect efficiently infect additional cell types expressing low levels of ACE2. The B.1.351 variant has evolved to reshape antigenic surfaces of the major neutralizing sites on the S protein, rendering complete resistance to some potent neutralizing antibodies. These findings provide structural details on how the wide spread of SARS-CoV-2 enables rapid evolution to enhance viral fitness and immune evasion. They may guide intervention strategies to control the pandemic.
ABSTRACT
Substitution for aspartic acid by glycine at position 614 in the spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the ongoing pandemic, appears to facilitate rapid viral spread. The G614 variant has now replaced the D614-carrying virus as the dominant circulating strain. We report here cryo-EM structures of a full-length S trimer carrying G614, which adopts three distinct prefusion conformations differing primarily by the position of one receptor-binding domain (RBD). A loop disordered in the D614 S trimer wedges between domains within a protomer in the G614 spike. This added interaction appears to prevent premature dissociation of the G614 trimer, effectively increasing the number of functional spikes and enhancing infectivity. The loop transition may also modulate structural rearrangements of S protein required for membrane fusion. These findings extend our understanding of viral entry and suggest an improved immunogen for vaccine development.
ABSTRACT
Effective intervention strategies are urgently needed to control the COVID-19 pandemic. Human angiotensin-converting enzyme 2 (ACE2) is a carboxypeptidase that forms a dimer and serves as the cellular receptor for SARS-CoV-2. It is also a key negative regulator of the renin-angiotensin system (RAS), conserved in mammals, which modulates vascular functions. We report here the properties of a trimeric ACE2 variant, created by a structure-based approach, with binding affinity of ~60 pM for the spike (S) protein of SARS-CoV-2, while preserving the wildtype peptidase activity as well as the ability to block activation of angiotensin II receptor type 1 in the RAS. Moreover, the engineered ACE2 potently inhibits infection of SARS-CoV-2 in cell culture. These results suggest that engineered, trimeric ACE2 may be a promising anti-SARS-CoV-2 agent for treating COVID-19.
ABSTRACT
The chemical constituents of Taxus chinensis var. mairei cell cultures were investigated by chromatographic methods, including silica gel column chromatography, Sephadex LH-20 and preparative HPLC. Thirteen compounds were isolated from the 80% ethanol extract of cultured cells and their structures were elucidated by spectral data and physicochemical properties, which were identified as 2α,4α,7β,9α,10β-pentaacetoxy-14β-hydroxytax-11-ene (1), 2α,4α,7β,9α,10β-pentaacetoxytax-11-ene (2), 1β-deoxybaccatin VI (3), 2α-acetoxytaxusin (4), taxuyunnanine C (5), yunnanxane (6), 2α,5α,10β-triacetoxy-14β-propionyloxy-4 (20), 11-taxadiene (7), 2α,5α,10β-triacetoxy-14β-isobutyryloxy-4 (20), 11-taxadiene (8), 2α,5α,10β-triacetoxy-14β-(2'-methyl)butyryloxy-4 (20), 11-taxadiene (9), 13-dehydroxylbaccatin III (10), 13-dehydroxy-10-deacetylbaccatin III (11), paclitaxel (12) and (13) β-sitosterol. Among them, compound 1 is a new compound, and compounds 2, 4, 10 and 11 are isolated from the cell culture of Taxus chinensis var. mairei for the first time.
ABSTRACT
To study the protective effect and preliminary mechanisms of asiatic acid against oxygen-glucose deprivation/reoxygenation (OGD/R) injury of PC12 cells, Na2S2O4 combined with low glucose induced damage of PC12 cells was served as OGD/R injury model in vitro. MTT method was used to evaluate cell survival. Ultraviolet spectrophotometry was performed to determine lactate dehydrogenase (LDH) leakage, lactic acid (LD) content, intracellular superoxide dismutase (SOD), malonyldialdehyde (MDA), and cellular Caspase-3 activity. Flow cytometry was applied to assay cell apoptosis. Na2S2O4 combined with low glucose induced significant cell survival rate decreasing compared with normal cells. Cell survival rate increasing, LDH leakage alleviating, LD producing inhibiting, SOD activity promotion, MDA content reducing, cell apoptotic rate decreasing and Caspase-3 activity inhibiting were observed when cells were preincubated with different concentration of asiatic acid (10, 1 and 0.1 micromol x L(-1)). Evident protective effect of asiatic acid against OGD/R injured PC12 cells was verified in our experiment, and the possible mechanisms were related to eliminating free radicals and inhibiting cell apoptosis.
ABSTRACT
Objective To study the effects of Levodopa on the abnormal behavior, nigral antioxidation system, mitochondrial respiration-chain function, neurotransmitter metabolism of Parkinson's disease (PD) model rat and its mechanism.Methods The rat models of PD were established through stereotaxic microinjection of 6-hydroxydopamine (6-OHDA). The rats in levodopa group were given levodopa 25 mg/(kg?d) through intragastric administration for 45 days. All the rats’behavior was tested before and after giving medicine. The activity of glutathione peroxidase(GSH-Px) and ROS, contents of malondialdedyde(MDA) and mitochondrial respiratory chain enzyme complex Ⅰ in nigra and the contents of dopamine(DA), homovanillic acid(HVA) and activity of monoamine oxidase-B(MAO-B) in caudate nucleus were assayed after treatment.Results (1) Compared with before treatment, the rotation rate after treatment decreased obviously( P
ABSTRACT
Objective To explore the role of intravenous nutrition and enteral nutrition in the treatment of gastroplegia after gastrectomy. Methods The clinical data of 63 cases of gastroplegia after gastrectomy were retrospectively analyzed. Among the 63 cases, 30 were treated by gastrodynamic drugs and intravenous nutrition(intravenous nutrition group), and the other 33 cases were treated by gastrodynamic drugs and enteral nutrition(enteral nutrition group). Gastrointestinal decompression amount and recovery time of gastroplegia between the two groups were compared. Results Enteral nutrition group had a short recovery time of gastroplegia and less gastrointestinal decompression amount compared with intravenous nutrition group(P
