ABSTRACT
The human membrane protein Angiotensin-converting enzyme 2 (hACE2) acts as the main receptor for host cells invasion of the new coronavirus SARS-CoV-2. The viral surface glycoprotein Spike binds to hACE2, which triggers virus entry into cells. As of today, the role of hACE2 for virus fusion is not well understood. Blocking the transition of Spike from its prefusion to post-fusion state might be a strategy to prevent or treat COVID-19. Here we report a single particle cryo-electron microscopy analysis of SARS-CoV-2 trimeric Spike in presence of the human ACE2 ectodomain. The binding of purified hACE2 ectodomain to Spike induces the disassembly of the trimeric form of Spike and a structural rearrangement of its S1 domain to form a stable, monomeric complex with hACE2. This observed hACE2 dependent dissociation of the Spike trimer suggests a mechanism for the therapeutic role of recombinant soluble hACE2 for treatment of COVID-19.
Subject(s)
COVID-19ABSTRACT
The drastic increase in the number of coronaviruses discovered and coronavirus genomes being sequenced have given us a great opportunity to perform genomics and bioinformatics analysis on this family of viruses. Coronaviruses possess the largest genomes (26.4 to 31.7 kb) among all known RNA viruses, with G + C contents varying from 32% to 43%. Phylogenetically, three genera, Alphacoronavirus, Betacoronavirus and Gammacoronavirus, with Betacoronavirus consisting of subgroups A, B, C were known to exist but now a new genus D also exists,namely the Deltacoronavirus. In such a situation, it becomes highly important for efficient classification of all virus data so that it helps us in suitable planning,containment and treatment. The objective of this paper is to classify SARS corona-virus nucleotide sequences based on parameters such as sequence length, percentage similarity between the sequence information,open and closed gaps in the sequence due to multiple mutations and many others. By doing this, we will be able to predict accurately the similarity of SARS CoV-2 virus with respect to other corona-viruses like the Wuhan corona-virus, the bat corona-virus and the pneumonia virus and would help us better understand about the taxonomy of the corona-virus family.
Subject(s)
PneumoniaABSTRACT
Effective and safe vaccines against SARS-CoV-2 are highly desirable to prevent casualties and societal cost caused by Covid-19 pandemic. The receptor binding domain (RBD) of the surface-exposed spike protein of SARS-CoV-2 represents a suitable target for the induction of neutralizing antibodies upon vaccination. Small protein antigens typically induce weak immune response while particles measuring tens of nanometers are efficiently presented to B cell follicles and subsequently to follicular germinal center B cells in draining lymph nodes, where B cell proliferation and affinity maturation occurs. Here we prepared and analyzed the response to several DNA vaccines based on genetic fusions of RBD to four different scaffolding domains, namely to the foldon peptide, ferritin, lumazine synthase and {beta}-annulus peptide, presenting from 6 to 60 copies of the RBD on each particle. Scaffolding strongly augmented the immune response with production of neutralizing antibodies and T cell response including cytotoxic lymphocytes in mice upon immunization with DNA plasmids. The most potent response was observed for the 24-residue {beta}-annulus peptide scaffold that forms large soluble assemblies, that has the advantage of low immunogenicity in comparison to larger scaffolds. Our results support the advancement of this vaccine platform towards clinical trials.
Subject(s)
COVID-19ABSTRACT
We have determined SARS-CoV-2-specific antibody responses in a cohort of 96 individuals with acute infection and in 578 individuals enrolled in a seroprevalence population study in Switzerland including three groups, i.e. subjects with previous RT-PCR confirmed SARS-CoV-2 infections (n=90), positive patient contacts (n=177) and random selected subjects (n=311). SARS-CoV-2 antibody responses specific to the Spike (S), in the monomeric and native trimeric forms, and/or the nucleocapsid (N) proteins were equally sensitive in the acute infection phase. Interestingly, as compared to anti-S antibody responses, those against the N protein appear to wane in the post-infection and substantially underestimated the proportion of SARS-CoV-2 infections in the groups of patient positive contacts, i.e. 10.9 to 32.2% reduction and in the random selected general population, i.e. up to 45% reduction. The overall reduction in seroprevalence targeting only anti-N IgG antibodies for the total cohort ranged from 9.4 to 31%. Of note, the use of the S protein in its native trimer form was more sensitive as compared to monomeric S proteins. These results indicate that the assessment of anti-S IgG antibody responses against the native trimeric S protein should be implemented to estimate SARS-CoV-2 infections in population-based seroprevalence studies.
Subject(s)
COVID-19ABSTRACT
We describe the evolution of severe acute respiratory coronavirus 2 (SARS-CoV-2) seroprevalence in the greater area of Zurich, Switzerland, a region that has been only mildly hit by the pandemic in spite of hosting an international airport hub and a highly mobile population. Seroprevalence studies in low-prevalence settings require large sample sizes and high-specificity methodologies. To address this particular challenge, we developed a Tripartite Automated Blood Immunoassay to assess the IgG response against three SARS-CoV-2 proteins on approximately 40'000 samples from university hospital patients and healthy blood donors. The seroprevalence increased in March 2020 (0.3%; CI95%: 0.1% - 0.5%) in the cohort of the hospital patients but rapidly plateaued in April at 1.1-1.3%, with a slight drop in June, then decreased in July to 0.3-0.7%. Seropositive samples were confirmed with Western Blotting and liquid-phase binding assays. Employing a dynamic transmission model that describes SARS-CoV-2 transmission and seroconversion in the general population of the Canton of Zurich, we estimated an infection fatality ratio of 0.6% (CI95%: 0.4%-0.8%). We conclude that a small proportion of the population in the greater area of Zurich has been exposed to SARS-CoV-2, with an IFR that is similar to that of other European areas. The evolution of seroprevalence points to a high effectiveness of containment measures and/or to rapid loss of humoral responses.