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
Optimal immune responses furnish long-lasting (durable) antibodies protective across dynamically mutating viral variants (broad). To assess robustness of mRNA vaccine-induced immunity, we compared antibody durability and breadth after SARS-CoV-2 infection and vaccination. While vaccination delivered robust initial virus-specific antibodies with some cross-variant coverage, pre-variant SARS-CoV-2 infection-induced antibodies, while modest in magnitude, showed highly stable long-term antibody dynamics. Vaccination after infection induced maximal antibody magnitudes with enhanced longitudinal stability while infection-naive vaccinee antibodies fell with time to post-infection-alone levels. The composition of antibody neutralizing activity to variant relative to original virus also differed between groups, with infection-induced antibodies demonstrating greater relative breadth. Differential antibody durability trajectories favored COVID-19-recovered subjects with dual memory B cell features of greater early antibody somatic mutation and cross-coronavirus reactivity. By illuminating an infection-mediated antibody breadth advantage and an anti-SARS-CoV-2 antibody durability-enhancing function conferred by recalled immunity, these findings may serve as guides for ongoing vaccine strategy improvement.
ABSTRACT
Memory B cell reserves can generate protective antibodies against repeated SARS-CoV-2 infections, but with an unknown reach from original infection to antigenically drifted variants. We charted memory B cell receptor-encoded monoclonal antibodies (mAbs) from 19 COVID-19 convalescent subjects against SARS-CoV-2 spike (S) and found 7 major mAb competition groups against epitopes recurrently targeted across individuals. Inclusion of published and newly determined structures of mAb-S complexes identified corresponding epitopic regions. Group assignment correlated with cross-CoV-reactivity breadth, neutralization potency, and convergent antibody signatures. mAbs that competed for binding the original S isolate bound differentially to S variants, suggesting the protective importance of otherwise-redundant recognition. The results furnish a global atlas of the S-specific memory B cell repertoire and illustrate properties conferring robustness against emerging SARS-CoV-2 variants.
ABSTRACT
The current COVID-19 pandemic is caused by the SARS-CoV-2 betacoronavirus, which utilizes its highly glycosylated trimeric Spike protein to bind to the cell surface receptor ACE2 glycoprotein and facilitate host cell entry. We utilized glycomics-informed glycoproteomics to characterize site-specific microheterogeneity of glycosylation for a recombinant trimer Spike mimetic immunogen and for a soluble version of human ACE2. We combined this information with bioinformatic analyses of natural variants and with existing 3D-structures of both glycoproteins to generate molecular dynamics simulations of each glycoprotein alone and interacting with one another. Our results highlight roles for glycans in sterically masking polypeptide epitopes and directly modulating Spike-ACE2 interactions. Furthermore, our results illustrate the impact of viral evolution and divergence on Spike glycosylation, as well as the influence of natural variants on ACE2 receptor glycosylation that, taken together, can facilitate immunogen design to achieve antibody neutralization and inform therapeutic strategies to inhibit viral infection.
ABSTRACT
The COVID-19 pandemic continues to infect millions of people worldwide. In order to curb its spread and reduce morbidity and mortality, it is essential to develop sensitive and quantitative methods that identify infected individuals and enable accurate population-wide screening of both past and present infection. Here we show that Single Molecule Array assays detect seroconversion in COVID-19 patients as soon as one day after symptom onset using less than a microliter of blood. This multiplexed assay format allows us to quantitate IgG, IgM and IgA immunoglobulins against four SARS-CoV-2 targets, thereby interrogating 12 antibody isotype-viral protein interactions to give a high resolution profile of the immune response. Using a cohort of samples collected prior to the outbreak as well as samples collected during the pandemic, we demonstrate a sensitivity of 86% and a specificity of 100% during the first week of infection, and 100% sensitivity and specificity thereafter. This assay should become the gold standard for COVID19 serological profiling and will be a valuable tool for answering important questions about the heterogeneity of clinical presentation seen in the ongoing pandemic.
ABSTRACT
The ongoing SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) pandemic has created urgent needs for intervention strategies to control the crisis. The spike (S) protein of the virus forms a trimer and catalyzes fusion between viral and target cell membranes - the first key step of viral infection. Here we report two cryo-EM structures, both derived from a single preparation of the full-length S protein, representing the prefusion (3.1[A] resolution) and postfusion (3.3[A] resolution) conformations, respectively. The spontaneous structural transition to the postfusion state under mild conditions is independent of target cells. The prefusion trimer forms a tightly packed structure with three receptor-binding domains clamped down by a segment adjacent to the fusion peptide, significantly different from recently published structures of a stabilized S ectodomain trimer. The postfusion conformation is a rigid tower-like trimer, but decorated by N-linked glycans along its long axis with almost even spacing, suggesting possible involvement in a mechanism protecting the virus from host immune responses and harsh external conditions. These findings advance our understanding of how SARS-CoV-2 enters a host cell and may guide development of vaccines and therapeutics.
ABSTRACT
Objective To establish a rapid and accurate method, and to determine the density of mice and rats sperm with enzyme-labeled instrument.Methods ①The optimal wavelengths and the regression equation set up: After six Kunming mice and six Sprague-Dawley rats were sacrificed, the left epididymis was separated and fully cut up in phosphate buffer saline.With water bath, the sperm were fully dissociated.Using the enzyme-labeled instrument to detect the wavelength absorbance respectively under different wavelength and fitting absorbance curve.The best wavelength will be the most close to 1 of the correlation coefficient ( R2 ) and the standard deviation of minimum.After ten Kunming mice and ten Sprague-Dawley rats were sacrificed,the sperm suspension of different concentration gradient were got.The regression equation of the sperm density and absorbance was established by using enzyme-labeled instrument and haemocytometer.②The test of sperm absorbance stability: Mice and rats,six respectively,were used to make the sperm suspension.Samples were put in room temperature (25℃) or 37℃water bath continued,and after water bath about 0,20,30,40,50, 60 min,the change of absorbance was recorded.③The regression equation verification:The mice were administrated orally with 20% ethanol solution for 30 days to make oligospermia.In order to verify the new method, two different method were used to get the sample sperm.Results The optimal absorbancy-sperm density curve could be established at 380 nm.The means of KM mice sperm count ( x1 ) and absorbance ( y1 ) are showed to be the linear function,and the linear regression equation is y1 =2 ×10 -9 x1 +0.0648, R2 =0.9743.The means of SD rat sperm count ( x2 ) and absorbance (y2) are showed to be the linear function,and the linear regression equation is y2 =5 ×10 -9x2 +0.0621,R2 =0.9940.SD rat sperm suspension liquid after 60 min in water bath, absorbance value at 0 min significantly decreased(P<0.05), but at room temperature after 40 min significantly increased ( P<0.05); KM mice sperm suspension in the water bath and under the condition of normal temperature after 50 min, compared with the 0 min, absorbance value increased significantly(P<0.05).Compared with control group, sperm density of ethanol oligozoospermia group by enzyme standard detector and standard curve calculation were significantly decreased ( P <0.05 );compared with absorbancy-sperm density equation, determination of ethanol oligozoospermia group of sperm density by cell counting plate method had not significant difference.The results suggested absorbancy-sperm density equation could effectively detect the reduction of the mice sperm in oligospermia.Conclusion Using enzyme-labeled instrument to set up the curve of absorbancy-sperm density equation can estimate the sperm density of mice and rats rapidly and exactly.