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1.
Nat Commun ; 13(1): 1178, 2022 03 04.
Article in English | MEDLINE | ID: covidwho-1730285

ABSTRACT

Recently emerged variants of SARS-CoV-2 contain in their surface spike glycoproteins multiple substitutions associated with increased transmission and resistance to neutralising antibodies. We have examined the structure and receptor binding properties of spike proteins from the B.1.1.7 (Alpha) and B.1.351 (Beta) variants to better understand the evolution of the virus in humans. Spikes of both variants have the same mutation, N501Y, in the receptor-binding domains. This substitution confers tighter ACE2 binding, dependent on the common earlier substitution, D614G. Each variant spike has acquired other key changes in structure that likely impact virus pathogenesis. The spike from the Alpha variant is more stable against disruption upon binding ACE2 receptor than all other spikes studied. This feature is linked to the acquisition of a more basic substitution at the S1-S2 furin site (also observed for the variants of concern Delta, Kappa, and Omicron) which allows for near-complete cleavage. In the Beta variant spike, the presence of a new substitution, K417N (also observed in the Omicron variant), in combination with the D614G, stabilises a more open spike trimer, a conformation required for receptor binding. Our observations suggest ways these viruses have evolved to achieve greater transmissibility in humans.


Subject(s)
Angiotensin-Converting Enzyme 2/metabolism , COVID-19/metabolism , Mutation, Missense , SARS-CoV-2/genetics , Spike Glycoprotein, Coronavirus/genetics , Angiotensin-Converting Enzyme 2/chemistry , Angiotensin-Converting Enzyme 2/ultrastructure , Binding Sites/genetics , COVID-19/transmission , COVID-19/virology , Cryoelectron Microscopy , Cytopathogenic Effect, Viral/genetics , Evolution, Molecular , Host-Pathogen Interactions , Humans , Kinetics , Models, Molecular , Protein Binding , Protein Domains , SARS-CoV-2/metabolism , SARS-CoV-2/physiology , Spike Glycoprotein, Coronavirus/chemistry , Spike Glycoprotein, Coronavirus/metabolism
2.
Semin Immunol ; 55: 101507, 2021 06.
Article in English | MEDLINE | ID: covidwho-1492624

ABSTRACT

Coronaviruses are evolutionarily successful RNA viruses, common to multiple avian, amphibian and mammalian hosts. Despite their ubiquity and potential impact, knowledge of host immunity to coronaviruses remains incomplete, partly owing to the lack of overt pathogenicity of endemic human coronaviruses (HCoVs), which typically cause common colds. However, the need for deeper understanding became pressing with the zoonotic introduction of three novel coronaviruses in the past two decades, causing severe acute respiratory syndromes in humans, and the unfolding pandemic of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This renewed interest not only triggered the discovery of two of the four HCoVs, but also uncovered substantial cellular and humoral cross-reactivity with shared or related coronaviral antigens. Here, we review the evidence for cross-reactive B cell memory elicited by HCoVs and its potential impact on the puzzlingly variable outcome of SARS-CoV-2 infection. The available data indicate targeting of highly conserved regions primarily in the S2 subunits of the spike glycoproteins of HCoVs and SARS-CoV-2 by cross-reactive B cells and antibodies. Rare monoclonal antibodies reactive with conserved S2 epitopes and with potent virus neutralising activity have been cloned, underscoring the potential functional relevance of cross-reactivity. We discuss B cell and antibody cross-reactivity in the broader context of heterologous humoral immunity to coronaviruses, as well as the limits of protective immune memory against homologous re-infection. Given the bidirectional nature of cross-reactivity, the unprecedented current vaccination campaign against SARS-CoV-2 is expected to impact HCoVs, as well as future zoonotic coronaviruses attempting to cross the species barrier. However, emerging SARS-CoV-2 variants with resistance to neutralisation by vaccine-induced antibodies highlight a need for targeting more constrained, less mutable parts of the spike. The delineation of such cross-reactive areas, which humoral immunity can be trained to attack, may offer the key to permanently shifting the balance of our interaction with current and future coronaviruses in our favour.


Subject(s)
COVID-19 , SARS-CoV-2 , Animals , Antibodies, Viral , Humans , Immunity, Humoral
3.
Sci Adv ; 7(22)2021 05.
Article in English | MEDLINE | ID: covidwho-1388434

ABSTRACT

The coronaviral spike is the dominant viral antigen and the target of neutralizing antibodies. We show that SARS-CoV-2 spike binds biliverdin and bilirubin, the tetrapyrrole products of heme metabolism, with nanomolar affinity. Using cryo-electron microscopy and x-ray crystallography, we mapped the tetrapyrrole interaction pocket to a deep cleft on the spike N-terminal domain (NTD). At physiological concentrations, biliverdin significantly dampened the reactivity of SARS-CoV-2 spike with immune sera and inhibited a subset of neutralizing antibodies. Access to the tetrapyrrole-sensitive epitope is gated by a flexible loop on the distal face of the NTD. Accompanied by profound conformational changes in the NTD, antibody binding requires relocation of the gating loop, which folds into the cleft vacated by the metabolite. Our results indicate that SARS-CoV-2 spike NTD harbors a dominant epitope, access to which can be controlled by an allosteric mechanism that is regulated through recruitment of a metabolite.


Subject(s)
COVID-19/immunology , Heme/metabolism , Spike Glycoprotein, Coronavirus/chemistry , Spike Glycoprotein, Coronavirus/immunology , Spike Glycoprotein, Coronavirus/metabolism , Antibodies, Monoclonal/immunology , Antibodies, Monoclonal/metabolism , Antibodies, Neutralizing/immunology , Bilirubin/metabolism , Biliverdine/metabolism , Cryoelectron Microscopy , Crystallography, X-Ray , Epitopes , Humans , Immune Sera , SARS-CoV-2/immunology , SARS-CoV-2/pathogenicity
4.
Nat Struct Mol Biol ; 27(10): 1001, 2020 Oct.
Article in English | MEDLINE | ID: covidwho-1387443

ABSTRACT

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

5.
Nat Commun ; 11(1): 5337, 2020 10 21.
Article in English | MEDLINE | ID: covidwho-1387319

ABSTRACT

The CR3022 antibody, selected from a group of SARS-CoV monoclonal antibodies for its ability to cross-react with SARS-CoV-2, has been examined for its ability to bind to the ectodomain of the SARS-CoV-2 spike glycoprotein. Using cryo-electron microscopy we show that antibody binding requires rearrangements in the S1 domain that result in dissociation of the spike.


Subject(s)
Antibodies, Monoclonal/immunology , Antibodies, Viral/immunology , Betacoronavirus/immunology , Binding Sites, Antibody/immunology , Spike Glycoprotein, Coronavirus/immunology , Animals , COVID-19 , Cell Line , Chlorocebus aethiops , Coronavirus Infections/virology , Cryoelectron Microscopy , Humans , Neutralization Tests , Pandemics , Pneumonia, Viral/virology , Protein Domains/immunology , SARS-CoV-2 , Vero Cells
6.
Proc Natl Acad Sci U S A ; 118(9)2021 03 02.
Article in English | MEDLINE | ID: covidwho-1080743

ABSTRACT

The majority of currently circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viruses have mutant spike glycoproteins that contain the D614G substitution. Several studies have suggested that spikes with this substitution are associated with higher virus infectivity. We use cryo-electron microscopy to compare G614 and D614 spikes and show that the G614 mutant spike adopts a range of more open conformations that may facilitate binding to the SARS-CoV-2 receptor, ACE2, and the subsequent structural rearrangements required for viral membrane fusion.


Subject(s)
COVID-19/virology , SARS-CoV-2/chemistry , Spike Glycoprotein, Coronavirus/chemistry , Cryoelectron Microscopy , Humans , Protein Conformation , SARS-CoV-2/genetics , Spike Glycoprotein, Coronavirus/genetics , Virus Internalization
7.
Nat Commun ; 12(1): 837, 2021 02 05.
Article in English | MEDLINE | ID: covidwho-1065863

ABSTRACT

Coronaviruses of bats and pangolins have been implicated in the origin and evolution of the pandemic SARS-CoV-2. We show that spikes from Guangdong Pangolin-CoVs, closely related to SARS-CoV-2, bind strongly to human and pangolin ACE2 receptors. We also report the cryo-EM structure of a Pangolin-CoV spike protein and show it adopts a fully-closed conformation and that, aside from the Receptor-Binding Domain, it resembles the spike of a bat coronavirus RaTG13 more than that of SARS-CoV-2.


Subject(s)
COVID-19/prevention & control , Evolution, Molecular , SARS-CoV-2/genetics , Spike Glycoprotein, Coronavirus/genetics , Angiotensin-Converting Enzyme 2/metabolism , Animals , Binding, Competitive , COVID-19/epidemiology , COVID-19/virology , Cryoelectron Microscopy , Humans , Models, Molecular , Pandemics , Pangolins/virology , Protein Binding , Protein Domains , SARS-CoV-2/metabolism , SARS-CoV-2/physiology , Spike Glycoprotein, Coronavirus/chemistry , Spike Glycoprotein, Coronavirus/metabolism
8.
Science ; 370(6522): 1339-1343, 2020 12 11.
Article in English | MEDLINE | ID: covidwho-913669

ABSTRACT

Zoonotic introduction of novel coronaviruses may encounter preexisting immunity in humans. Using diverse assays for antibodies recognizing SARS-CoV-2 proteins, we detected preexisting humoral immunity. SARS-CoV-2 spike glycoprotein (S)-reactive antibodies were detectable using a flow cytometry-based method in SARS-CoV-2-uninfected individuals and were particularly prevalent in children and adolescents. They were predominantly of the immunoglobulin G (IgG) class and targeted the S2 subunit. By contrast, SARS-CoV-2 infection induced higher titers of SARS-CoV-2 S-reactive IgG antibodies targeting both the S1 and S2 subunits, and concomitant IgM and IgA antibodies, lasting throughout the observation period. SARS-CoV-2-uninfected donor sera exhibited specific neutralizing activity against SARS-CoV-2 and SARS-CoV-2 S pseudotypes. Distinguishing preexisting and de novo immunity will be critical for our understanding of susceptibility to and the natural course of SARS-CoV-2 infection.


Subject(s)
Antibodies, Viral/blood , COVID-19/immunology , Immunity, Humoral , SARS-CoV-2/immunology , Spike Glycoprotein, Coronavirus/immunology , Adult , Aged , Aged, 80 and over , Amino Acid Sequence , Animals , COVID-19/blood , Epitope Mapping , Female , HEK293 Cells , Humans , Immunoglobulin A/blood , Immunoglobulin G/blood , Immunoglobulin M/blood , Male , Middle Aged , SARS-CoV-2/chemistry , Spike Glycoprotein, Coronavirus/chemistry , Viral Zoonoses/blood , Viral Zoonoses/immunology , Young Adult
9.
Nat Genet ; 52(12): 1294-1302, 2020 12.
Article in English | MEDLINE | ID: covidwho-880696

ABSTRACT

Angiotensin-converting enzyme 2 (ACE2) is an entry receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and a regulator of several physiological processes. ACE2 has recently been proposed to be interferon (IFN) inducible, suggesting that SARS-CoV-2 may exploit this phenomenon to enhance viral spread and questioning the efficacy of IFN treatment in coronavirus disease 2019. Using a recent de novo transcript assembly that captured previously unannotated transcripts, we describe a new isoform of ACE2, generated by co-option of intronic retroelements as promoter and alternative exon. The new transcript, termed MIRb-ACE2, exhibits specific expression patterns across the aerodigestive and gastrointestinal tracts and is highly responsive to IFN stimulation. In contrast, canonical ACE2 expression is unresponsive to IFN stimulation. Moreover, the MIRb-ACE2 translation product is a truncated, unstable ACE2 form, lacking domains required for SARS-CoV-2 binding and is therefore unlikely to contribute to or enhance viral infection.


Subject(s)
Angiotensin-Converting Enzyme 2/biosynthesis , Interferons/metabolism , Retroelements/genetics , Angiotensin-Converting Enzyme 2/genetics , Animals , Cell Line , Chlorocebus aethiops , Enzyme Induction , Gene Expression Profiling , Gene Expression Regulation, Enzymologic , Gene Expression Regulation, Viral , HEK293 Cells , Humans , Isoenzymes/biosynthesis , Isoenzymes/genetics , Protein Stability , RNA-Seq , Receptors, Coronavirus/metabolism , SARS-CoV-2/metabolism , Tissue Distribution , Vero Cells
10.
Nature ; 588(7837): 327-330, 2020 12.
Article in English | MEDLINE | ID: covidwho-780015

ABSTRACT

Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is initiated by virus binding to the ACE2 cell-surface receptors1-4, followed by fusion of the virus and cell membranes to release the virus genome into the cell. Both receptor binding and membrane fusion activities are mediated by the virus spike glycoprotein5-7. As with other class-I membrane-fusion proteins, the spike protein is post-translationally cleaved, in this case by furin, into the S1 and S2 components that remain associated after cleavage8-10. Fusion activation after receptor binding is proposed to involve the exposure of a second proteolytic site (S2'), cleavage of which is required for the release of the fusion peptide11,12. Here we analyse the binding of ACE2 to the furin-cleaved form of the SARS-CoV-2 spike protein using cryo-electron microscopy. We classify ten different molecular species, including the unbound, closed spike trimer, the fully open ACE2-bound trimer and dissociated monomeric S1 bound to ACE2. The ten structures describe ACE2-binding events that destabilize the spike trimer, progressively opening up, and out, the individual S1 components. The opening process reduces S1 contacts and unshields the trimeric S2 core, priming the protein for fusion activation and dissociation of ACE2-bound S1 monomers. The structures also reveal refolding of an S1 subdomain after ACE2 binding that disrupts interactions with S2, which involves Asp61413-15 and leads to the destabilization of the structure of S2 proximal to the secondary (S2') cleavage site.


Subject(s)
Angiotensin-Converting Enzyme 2/chemistry , Angiotensin-Converting Enzyme 2/metabolism , Membrane Fusion/physiology , Protein Binding , Receptors, Coronavirus/metabolism , Spike Glycoprotein, Coronavirus/chemistry , Spike Glycoprotein, Coronavirus/metabolism , Angiotensin-Converting Enzyme 2/ultrastructure , Cryoelectron Microscopy , Furin/metabolism , Humans , Models, Molecular , Protein Folding , Protein Subunits/chemistry , Protein Subunits/metabolism , Proteolysis , Receptors, Coronavirus/chemistry , Receptors, Coronavirus/ultrastructure , Spike Glycoprotein, Coronavirus/ultrastructure
11.
Nat Struct Mol Biol ; 27(8): 763-767, 2020 08.
Article in English | MEDLINE | ID: covidwho-640223

ABSTRACT

SARS-CoV-2 is thought to have emerged from bats, possibly via a secondary host. Here, we investigate the relationship of spike (S) glycoprotein from SARS-CoV-2 with the S protein of a closely related bat virus, RaTG13. We determined cryo-EM structures for RaTG13 S and for both furin-cleaved and uncleaved SARS-CoV-2 S; we compared these with recently reported structures for uncleaved SARS-CoV-2 S. We also biochemically characterized their relative stabilities and affinities for the SARS-CoV-2 receptor ACE2. Although the overall structures of human and bat virus S proteins are similar, there are key differences in their properties, including a more stable precleavage form of human S and about 1,000-fold tighter binding of SARS-CoV-2 to human receptor. These observations suggest that cleavage at the furin-cleavage site decreases the overall stability of SARS-CoV-2 S and facilitates the adoption of the open conformation that is required for S to bind to the ACE2 receptor.


Subject(s)
Betacoronavirus/genetics , Host-Pathogen Interactions/genetics , Peptidyl-Dipeptidase A/chemistry , Receptors, Virus/chemistry , Spike Glycoprotein, Coronavirus/chemistry , Angiotensin-Converting Enzyme 2 , Animals , Betacoronavirus/metabolism , Betacoronavirus/ultrastructure , Binding Sites , COVID-19 , Chiroptera/virology , Coronavirus Infections/virology , Cryoelectron Microscopy , Evolution, Molecular , Furin/chemistry , Gene Expression , HEK293 Cells , Humans , Models, Molecular , Pandemics , Peptidyl-Dipeptidase A/genetics , Peptidyl-Dipeptidase A/metabolism , Pneumonia, Viral/virology , Protein Binding , Protein Conformation, alpha-Helical , Protein Conformation, beta-Strand , Protein Interaction Domains and Motifs , Protein Isoforms/chemistry , Protein Isoforms/genetics , Protein Isoforms/metabolism , Protein Stability , Proteolysis , Receptors, Virus/genetics , Receptors, Virus/metabolism , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , SARS-CoV-2 , Spike Glycoprotein, Coronavirus/genetics , Spike Glycoprotein, Coronavirus/metabolism , Structural Homology, Protein
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