Structural insights into coronavirus entry.

Structural insights into coronavirus entry.

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Coronaviruses (CoVs) have caused outbreaks of deadly pneumonia in humans since the beginning of the 21st century. The severe acute respiratory syndrome coronavirus (SARS-CoV) emerged in 2002 and was responsible for an epidemic that spread to five continents with a fatality rate of 10% before being contained in 2003 (with additional cases reported in 2004). The Middle-East respiratory syndrome coronavirus (MERS-CoV) emerged in the Arabian Peninsula in 2012 and has caused recurrent outbreaks in humans with a fatality rate of 35%. SARS-CoV and MERS-CoV are zoonotic viruses that crossed the species barrier using bats/palm civets and dromedary camels, respectively. No specific treatments or vaccines have been approved against any of the six human coronaviruses, highlighting the need to investigate the principles governing viral entry and cross-species transmission as well as to prepare for zoonotic outbreaks which are likely to occur due to the large reservoir of CoVs found in mammals and birds. Here, we review our understanding of the infection mechanism used by coronaviruses derived from recent structural and biochemical studies.

Keywords: Coronavirus, Spike glycoprotein, Fusion protein, Membrane fusion, Proteolytic activation, Vaccine design


three dimensional
angiotensin-converting enzyme 2
amino-peptidase N
cryo-electron microscopy
dipeptidyl peptidase 4
antigen-binding fragment of an antibody
Middle-East respiratory syndrome coronavirus
mouse hepatitis virus
porcine δ-CoV
porcine epidemic diarrhea virus
severe acute respiratory syndrome coronavirus
transmissible gastroenteritis virus

1. Introduction

Coronaviruses (CoVs) are enveloped viruses with a positive sense RNA genome, that belong to the subfamily Coronavirinae within the family Coronaviridae, which is part of the Nidovirales order. They are classified in four genera (α, β, γ, and δ) and four lineages are recognized whithin the β-CoV genus (A, B, C and D). CoVs cause a variety of respiratory and enteric diseases in mammalian and avian species. Until recently, CoVs were considered to be pathogens with a largely veterinary relevance but with limited impact on human health. However, outbreaks of severe acute respiratory syndrome (SARS) in 2002–2004 and of Middle-East respiratory syndrome (MERS) starting in 2012, with fatality rates of 10% and 35%, respectively, led CoVs to be recognized as zoonotic threats with pandemic potential. Four other CoVs are endemic in the human population and cause up to 30% of mild respiratory tract infections as well as occasional severe disease in young children, the elderly or immunocompromised individuals (; ). These viruses are HCoV-NL63 and HCoV-229E (α-CoVs) as well as HCoV-OC43 and HCoV-HKU1 (β-CoVs). Numerous SARS-CoV and MERS-CoV-like viruses currently circulate in bats and dromedaries making outbreaks of highly pathogenic human CoVs a global health threat (; ; ; , ; ).

The CoV virion contains at least four structural proteins: spike (S), envelope (E), membrane (M) and nucleocapsid (N). In contrast to other β-CoV lineages, lineage A CoVs also encode a hemagglutinin–esterase which serves as receptor-destroying enzyme to facilitate release of viral progeny from infected cells and escape from attachment to non-permissive host cells or decoys (, ). S is a class 1 viral fusion protein that promotes host attachment and fusion of the viral and cellular membranes during entry (). As a consequence, S determines host range and cell tropism. S is also the main target of neutralizing antibodies elicited during infection and the focus of vaccine design. S is trimeric and each protomer is synthesized as a single polypeptide chain of 1100–1600 residues, depending on the CoV species. For many CoVs, S is processed by host proteases to generate two functional subunits, designated S1 and S2, which remain non-covalently bound in the prefusion conformation (). The S1 subunit comprises the apex of the S trimer, including the receptor-binding domains, and stabilizes the prefusion state of the S2 fusion machinery, which is anchored in the viral membrane. For all CoVs, S is further cleaved by host proteases at the so-called S2’ site located immediately upstream of the fusion peptide. This cleavage has been proposed to activate the protein for membrane fusion via large-scale, irreversible conformational changes (; ).

Although several class 1 viral fusion proteins have been extensively studied, CoV S proteins have proven reluctant to structural characterization until recently. Structural studies were largely limited to X-ray crystallographic analysis of isolated receptor-binding domains in complex with viral receptor ectodomains or neutralizing antibodies (; ; ; ; ; ; ; ; ) and of the S2 postfusion core (; ; ; , ; ) with the exception of two low-resolution electron microscopy reports (, ). In the past few years, however, technical advances in single-particle cryo-electron microscopy (cryoEM) (; ; , ; ; ; ) together with the implementation of strategies for the stabilization of CoV S proteins in prefusion conformation (; ) led to a surge of structural data for multiple S ectodomain trimers. We review here our current understanding of the mechanism used by CoVs to infect host cells based on recent structural and biochemical studies of S glycoprotein ectodomains in prefusion and postfusion states as well as complexes with known receptors or neutralizing antibodies.

2. Prefusion S architecture

CryoEM studies of the S glycoproteins of mouse hepatitis virus (MHV) and HKU1 led to the first structures at high-enough resolution to obtain an atomic model of the prefusion state (; ). These structures revealed that prefusion S ectodomains are ~ 160 Å-long trimers with a triangular cross-section (Fig. 1A and B).

CryoEM structure of the apo-HCoV-OC43 S glycoprotein. (A) Ribbon diagrams of the apo HCoV-OC43 S ectodomain trimer (PDB: 6OHW) in two orthogonal orientations, from the side (left) and from the top, looking towards the viral membrane (right). (B) Side view of one S protomer. (C) Ribbon diagram of the HCoV-OC43 S1 subunit. (D–E) Close-up view of HCoV-OC43 domain A (D) and domain B (E). (F) Ribbon diagram of the HCoV-OC43 S2 subunit in the prefusion conformation. The N- and C-termini are labeled in panels (B–E).

The S1 subunit adopts a “V” shaped architecture for β and γ CoVs (; ; ; ; ; ) (Fig. 1C), or a square-shaped organization for α- and δ-CoVs (; ; ). The S1 subunit folds as β-rich domains designated A, B, C, D. Several α-CoVs harbor a likely duplication of their domain A at the N-terminus of the S glycoprotein (; ). This additional domain, designated domain 0, was visualized in the NL63 S structure and hypothesized to interact with heparan sulfate present at the host cell surface during viral entry (; ). Domain A and domain 0 adopt a galectin-like β-sandwich fold conserved across all CoV genera (; , ; ) (Fig. 1D). Domain B, which shows the highest sequence variability within CoV S1 subunits, has a markedly different architecture between α-, β-, γ- and δ-CoVs. B domains of β-CoVs contain a β-sheet core subdomain decorated with a highly variable external subdomain mediating receptor engagement (; ; ; ; ; ; ) (Fig. 1E). B domains of α-, γ- and δ-CoV form a β-sandwich decorated with loops mediating receptor attachment (; , ; ; ; ). In the context of the S trimer, β/γ CoV B domains interact with the A and B domains of another protomer, whereas they pack against the A domain of the same protomer in α/δ-CoVs (; , ; ).

The S2 subunit, which is more conserved than S1, comprises the fusion machinery and connects to the viral membrane. It is assembled from a large number of α-helices, an antiparallel core β-sheet, a β-rich connector domain and a stem helix leading to the heptad-repeat 2 (HR2) and the transmembrane region (Fig. 1F) (; , ; ; , ; ; , , ; ; ). Key S2 features facilitating virus-cell fusion include the fusion peptide, two heptad repeat regions (named HR1 and HR2) and the transmembrane domain. In the prefusion S conformation, a central helix stretches along the threefold axis, perpendicular to the viral membrane, and is located downstream the HR1 motif, which folds as four consecutive α-helices (; ). Moreover, an upstream helix runs parallel to and is zipped against the central helix via hydrophobic contacts (Fig. 1F). The CoV S2 subunit shares similarity with the pneumovirus/paramyxovirus F proteins—including a comparable 3D organization of the core β-sheet, the upstream helix and the central helix—suggesting an evolutionary relatedness between the viral fusion proteins of these different viruses and a conservation of their fusion mechanism (; , ; ; ; ).

A conserved tryptophan-rich segment (Y(V/I)KWPW(Y/W)VWL) directly preceding the CoV S transmembrane region is crucial for proper trimerization. This segment is also required functionally for formation of a fusion pore (). Furthermore, transmembrane domain interactions within and possibly between S trimers have been proposed to be essential to complete the membrane fusion process (). The transmembrane domain is followed by an intraviral/cytoplasmic tail of variable length (36–46 residues) depending on the coronavirus species, which contains a palmitoylated cysteine-rich region (of about 18–24 residues with 7–10 cysteines) and a variable C-terminal end (). The cytoplasmic tail is involved in assembly, intracellular transport, cell-surface expression and cell-cell fusion (; ; ; ; ; ; ). Currently, no structural information is available for any CoV full-length S, hindering our understanding of the influence of the transmembrane and cytoplasmic domains on the conformation of exposed antigenic sites, as previously studied for HIV-1 envelope (;).

3. Diversity of CoV receptors and entry mechanisms

CoV entry into susceptible cells is a complex process that requires the concerted action of receptor-binding and proteolytic processing of the S protein to promote virus-cell fusion (; ). Domain 0, domain A and/or domain B can act as receptor-binding domains and both attachment and entry receptors have been described, depending on the CoV species.

Lineage A β-CoVs attach via their S domain A to 5-N-acetyl-9-O-acetyl-sialosides (9-O-Ac-Sia) found on glycoproteins and glycolipids at the host cell surface to promote entry into susceptible cells (). These include human CoVs OC43 and HKU1, bovine CoV (BCoV) and porcine hemagglutinating encephalomyelitis virus. We recently identified and visualized by cryoEM the HCoV-OC43 S sialoside-binding site, which is located in a groove at the surface of domain A (Fig. 2A) (; ). This site is conserved in all other CoVs known to attach to 9-O-Ac-Sia (β-CoVs, lineage A) and shares architectural similarity with the ligand-binding pockets of CoV hemagglutinin-esterases and influenza virus C/D hemagglutinin-esterase-fusion glycoproteins, highlighting common structural principles of recognition (, ; ; ; ). The current consensus in the field is that HCoV-OC43 only utilizes 9-O-Ac-sialosides as host receptors. In line with this statement, ligand-interacting residues were shown to be essential for S-mediated viral entry (; ) and 9-O-Ac-Sia depletion from target cells resulted in severe decrease in virus infectivity (; ). Free 9-O-Ac-Sia, however, did not trigger S conformational changes associated with membrane fusion (). This observation contrasts with data for SARS-CoV S, for which addition of the human angiotensin-converting enzyme 2 (ACE2) ectodomain (the proteinaceous receptor) promoted S refolding to the postfusion state (; ). These findings suggested that either 9-O-Ac-Sia-containing receptors differ from proteinaceous receptors in their mode of action, or that an interaction with a yet unidentified proteinaceous receptor is required before or after virus internalization for HCoV-OC43 entry into target cells.

Structural studies of human CoV attachment to host receptors. (A–E), Ribbon diagrams of the complex between domain A of HCoV-OC43 S with a 9-O-Ac-Sia receptor analogue ((A) PDB: 6NZK), or the domain B of SARS-CoV S with ACE2 ((B) PDB: 2AJF), HCoV-NL63 S with ACE2 ((C) PDB: 3KBH), MERS-CoV S with DPP4 ((D) PDB: 4L72) and HCoV-229E S with APN ((E) PDB: 6ATK). In panels (B–E), each domain B is rendered in light blue and the receptor binding-motifs are colored purple.

The sialoside-binding site identified in HCoV-OC43 S is not conserved among CoVs which are also known to interact with sialoglycans to initiate host cell infection but are outside of the lineage A of β-CoVs, such as MERS-CoV (β-CoV, lineage C) or infectious bronchitis virus (IBV, δ-CoV) (; ). Some α-CoVs such as transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) use domain 0 to attach to sialoglycans, presumably to increase virus concentration at the cell surface and enhance subsequent attachment to proteinaceous receptors (; ). Carbohydrate binding via this domain has been proposed to be a determinant of the TGEV enteric tropism since loss of domain 0 appears to correlate with a loss of enteric tropism for porcine respiratory coronavirus (PRCoV), the latter virus being a naturally occurring TGEV variant ().

CoVs exploit a limited variety of proteinaceous receptors compared with the large number and diversity of viral species. All CoVs known to engage proteinaceous receptors do so using domain B with the exception of MHV, which binds CEACAM1a using domain A (; ; ). Remarkably, viruses from different genera, such as HCoV-NL63 (α-CoV) and SARS-CoV (β-CoV), can recognize the same region of ACE2 (entry receptor) using structurally distinct B domains (; , ; ). Many α-CoVs, including HCoV-229E, TGEV and PRCV, as well as porcine δ-CoV (PDCoV) utilize aminopeptidase N (APN) as entry receptor (; ; ; ; ; ) whereas MERS-CoV uses dipeptidyl peptidase 4 (DPP4) (; ; ). Crystal structures of SARS-CoV, HCoV-NL63, MERS-CoV, HCoV-229E B domains in complex with their cognate receptors provided atomic details of the interacting-interface and identified key residues for cross-species transmission and infection (Fig. 2) (; ; ; ; ). This information will be useful to guide the development of therapeutics and vaccines against human CoVs.

Recent cryoEM studies revealed that MERS-CoV S and SARS-CoV S can adopt open and closed conformations in which the receptor binding site of domain B is exposed and occluded, respectively (; ; ; ; ; ). In contrast, the MHV, HCoV-NL63, HCoV-HKU1, PDCoV, IBV and HCoV-OC43 S glycoproteins appear to only adopt a closed conformation (; , ; ; , ; ) and unknown trigger(s), besides proteolytic activation, might be necessary for these viruses to expose their receptor-binding motifs for recognition to occur. These findings suggest that CoVs have evolved a fine-tuned mechanism to balance masking of the receptor-binding motifs, putatively to avoid neutralization by the host humoral immune response, and their necessary exposure to enable receptor recognition and infection of host cells (, ; ).

Upon host recognition, CoVs are internalized via receptor-mediated clathrin-dependent, caveolin-dependent or other uptake pathways (; ; ; ). For instance, both clathrin-dependent and clathrin/caveolae-independent entry pathways have been reported for SARS-CoV (; ). Feline infectious peritonitis virus was suggested to enter host cells via a clathrin/caveolin-independent internalization route (; ) whereas a caveolin-dependent endocytic uptake has been suggested for HCoV-229E and HCoV-OC43 (; ).

4. S proteolytic cleavage

Several reports have demonstrated the key role of proteolytic processing of CoV S for cell-cell fusion activity and/or virus entry into host cells using experiments of inhibition of intracellular proteases (; ; ; ) and/or substitutions of residues at the S1/S2 or S2’ cleavage sites (; ; ; ; ).

Prior to and/or after uptake of the virion by a host cell, the S protein is proteolytically processed by host proteases at one or two cleavage sites and both receptor-binding and proteolytic processing act in synergy to induce large-scale S conformational changes promoting CoV entry. One of the cleavage sites is located at the boundary between the S1 and S2 subunits (S1/S2 cleavage site), whereas the other is located immediately upstream of the fusion peptide (S2’ cleavage site), reviewed in (). Cleavage at the S1/S2 site can occur upon viral egress, such as for MHV (), or upon encounter with a target cell, such as for SARS-CoV (; ; ), to yield two non-covalently associated subunits. This first cleavage event, along with binding to the host receptor, promotes further cleavage at the S2’ site for SARS-CoV S () and MERS-CoV S (;). Proteolysis at the conserved S2’ site is essential for fusion activation of all characterized CoV S proteins, and it can occur at the host membrane or in internal cellular compartments of the target cell (; ; ; ).

Cleavage at the MERS-CoV S1/S2 site by furin during viral egress enables subsequent exposure of the S2’ site upon binding to the host receptor and a second cleavage step by serine proteases anchored in the membrane of the target cells, eventually leading to fusion at the cytoplasmic membrane (early entry) (). Conversely, MERS-CoV budding with uncleaved S glycoproteins traffic to the endosomes of target cells where cathepsin L or other proteases promote membrane fusion (late entry) (). The former mechanism has been proposed to be the route of MERS-CoV entry into cell types relevant to lung infection, and therefore a significant determinant of MERS-CoV virulence (). Moreover, tetraspanin CD9 has been implicated in clustering DPP4 and transmembrane serine proteases to promote early entry of MERS-CoV (, ). PEDV, which replicates in the epithelial cells of the small intestine, undergoes S proteolytic activation by trypsin, which is highly abundant in the intestinal lumen (). The critical importance of cleavage at the S1/S2 site was also exemplified in studies with the MERS-CoV-related bat coronavirus HKU4. Although HKU4 S recognizes human DPP4, in vitro infectivity assays revealed that entry into human cells required addition of exogenous trypsin, suggesting proteolytic activation of this bat virus did not occur in human cells (). In line with these findings, various DPP4 mammalian orthologues, with variable binding affinities for the MERS-CoV S receptor-binding domain, were shown to support virus or pseudovirus entry into target cells in the presence of an activating protease (). These results collectively illustrate how specific S proteolytic cleavage participates in determining the intracellular site of fusion and also viral tropism and pathogenesis of CoVs. Therefore, the zoonotic potential of CoVs is not only determined by receptor engagement, but also by proteolytic processing of the S protein required for fusion activation.

5. Mechanism of fusion activation

We showed that in vitro trypsin cleavage of MHV, SARS-CoV and MERS-CoV S, under limited proteolysis conditions, recapitulated fusion activation by inducing the pre-to postfusion transition (). The cryoEM structure of the MHV S2 subunit ectodomain trimer revealed that membrane fusion involves large-scale S conformational changes that are reminiscent of the ones described for other class 1 fusion proteins, including the pneumovirus/paramyxovirus F glycoproteins (Fig. 3 ) (; , ; ; ). These experiments also demonstrated that (i) the S1 subunits stabilize the S2 fusion machinery in the spring-loaded, metastable prefusion state before initiation of infection; and (ii) postfusion S is the ground state of the fusion reaction. Similarly to the organization of influenza virus hemagglutinins (), domain B interacts with the HR1-central helix hairpin in prefusion closed S structures likely to stabilize S2 in the spring-loaded prefusion state. This interaction appears to coordinate receptor engagement with fusion. Upon receptor binding and proteolytic cleavage at the S1/S2 and S2′ sites, the S1 crown is likely shed (as observed for MERS-CoV S by ) to facilitate a conformational change of S2, which involves projection of the fusion peptide to a distance of ~ 100 Å and its insertion into the target membrane (Fig. 3) (, ). The free energy released upon S2 refolding from the prefusion to the postfusion state is believed to bring the viral and host membranes in close proximity and promote membrane merger ().

CoV S conformational changes driving the fusion reaction. (A), Ribbon diagram of the MHV S2 subunit in the prefusion conformation, PDB: 3JCL. (B), Ribbon diagram of the MHV S2 subunit in the postfusion conformation, PDB: 6B3O. The prefusion to postfusion transition involves a “jack-knife” refolding of the HR1 helices and intervening regions into a single continuous helix appended to the central helix. The connector domain and HR2 in the prefusion structure and the fusion peptide in the postfusion structure of MHV were not resolved and are therefore not shown.

Recent structural work comparing recombinant S proteins from SARS-CoV and MERS-CoV in isolation and in complex with their cognate receptors or neutralizing antibodies suggested an activation mechanism for coronavirus fusion (; ; ; ; ; ). Specifically, SARS-CoV and MERS-CoV S structures in complex with neutralizing antibodies isolated from survivors showed both antibodies competitively blocked receptor interaction, in agreement with previous surface plasmon resonance data (; ; ; ). The anti-SARS-CoV S230 antibody, however, functionally mimicked the receptor by promoting S fusogenic conformational rearrangements through a molecular ratcheting mechanism () (Fig. 4 ). These observations suggested that upon receptor recognition, bound B domains are locked in the open state, thereby releasing the constraints imposed on the HR1-central helix hairpin, allowing refolding of the S2 fusion machinery and membrane fusion to occur (; ; ; ) (Fig. 4). Proteolytic activation is likely required to ensure that S glycoproteins will work in synergy, with proper spatial and temporal coordination, to drive fusion of the viral and host membranes.

CryoEM structures of the SARS-CoV S glycoprotein in complex with the S230 neutralizing antibody. (A–B), Molecular surface representation of a complex with one open, one partially open, and one closed B domain, PDB: 6NB6 (left) and with three open B domains that do not follow threefold symmetry, PDB: 6NB7 (right). The structures are rendered with different colors for each S protomer (light blue, plum and gold) and the S230 Fab heavy (dark magenta) and light (magenta) chains (only the variable domains are shown).

6. Epitope masking and glycan shielding

A deep knowledge of the organization and chemical composition of carbohydrates obstructing the surface of CoV S glycoproteins is key for understanding accessibility to neutralizing antibodies and for guiding the rational development of subunit vaccines and therapeutics. S glycoproteins feature ~ 20–35 predicted N-linked oligosaccharides per protomer. A cryoEM structure of the HCoV-NL63 S ectodomain allowed to visualize for the first time the extensive N-linked glycans covering the surface of a CoV S trimer () (Fig. 5 ). A subsequent study revealed that numerous glycosylation sites are strictly or topologically conserved between PDCoV S and HCoV-NL63 S although the two glycoproteins share only 43% amino acid sequence identity and the two viruses belong to different genera infecting different hosts (). This observation suggested that all CoVs face similar immune pressure in their respective hosts, and that the areas that are masked by the conserved glycans might be key to the function of S. Based on the information gained from the HCoV-NL63 S structure, in which a glycan participates to masking the receptor-binding loops, it was proposed that the S glycan shield is involved in immune evasion, similarly to the well-characterized HIV-1 envelope trimer ().

Organization of the HCoV-NL63 S glycan shield. Ribbon representation of the S ectodomain trimer with N-linked glycans rendered as dark-blue spheres, PDB: 5SZS.

Comparison of the N-linked oligosaccharides of full-length MERS-CoV S derived from virions produced in African green monkey VeroE6 cells, or of a purified MERS-CoV S ectodomain recombinantly produced in HEK293F cells, revealed an extensive overlap of glycan composition, including the presence of hybrid and complex glycans (). Processed oligosaccharides were also observed decorating S trimers at the surface of authentic SARS-CoV virions (; ). These data indicated that at least a fraction of the MERS-CoV and SARS-CoV virions produced in a cell are exposed to the glycan-processing enzymes residing in the Golgi apparatus during assembly and budding, in contrast with previous models of CoV budding (; ).

A common feature observed in the glycosylation patterns of S glycoproteins is the presence of less densely glycosylated regions surrounding the S1/S2 cleavage site and the conserved fusion peptide, near the S2  cleavage site, probably to allow access to activating host proteases and for membrane fusion to take place (; ) (Fig. 5). These “glycan holes” could be targeted for epitope-focused immunogen design or new therapeutic development against CoV, as supported by the identification of a neutralization epitope within a comparable breach of the HIV-1 envelope glycan shield ().

7. Concluding remarks

Recent structural and functional characterization of CoV S glycoproteins provided insights into the mechanism used by these viruses to infect host cells and suggested possible strategies for rational design of vaccines and therapeutics. Introducing stabilizing mutations, which prevent the prefusion to postfusion S transition, led to the elicitation of improved neutralization titers in mice and will be a key tool for the design of subunit vaccines against CoVs (; ). Furthermore, the exposure of the fusion peptide at the surface of prefusion S trimers () and its conservation among CoVs indicate it might be an attractive target for broad inhibition of CoV entry. Major antigenic determinants of MHV and SARS-CoV S overlap with the fusion peptide region (; ) and binding of neutralizing antibodies to this site could putatively prevent fusogenic conformational changes, as proposed for influenza virus hemagglutinin or HIV envelope (; ; ). Finally, masking strain-specific antigenic regions via engineering of additional N-linked glycosylation sites, as implemented for the MERS-CoV domain B (), bears the promise of focusing the immune response on highly conserved epitopes and eliciting broadly neutralizing antibodies against CoVs.


We acknowledge support from the National Institute of General Medical Sciences (R01GM120553, D.V.), the National Institute of Allergy and Infectious Diseases (HHSN272201700059C, DV), a Pew Biomedical Scholars Award (D.V.), an Investigators in the Pathogenesis of Infectious Disease Award from the Burroughs Wellcome Fund (D.V.) and the Pasteur Institute (M.A.T.).


  • Bai X.C., Fernandez I.S., McMullan G., Scheres S.H. Ribosome structures to near-atomic resolution from thirty thousand cryo-EM particles. elife. 2013;2 [PMC free article] [PubMed] []
  • Bakkers M.J., Lang Y., Feitsma L.J., Hulswit R.J., de Poot S.A., van Vliet A.L., Margine I., de Groot-Mijnes J.D., van Kuppeveld F.J., Langereis M.A., Huizinga E.G., de Groot R.J. Betacoronavirus adaptation to humans involved progressive loss of hemagglutinin-esterase lectin activity. Cell Host Microbe. 2017;21:356. [PMC free article] [PubMed] []
  • Bakkers M.J., Zeng Q., Feitsma L.J., Hulswit R.J., Li Z., Westerbeke A., van Kuppeveld F.J., Boons G.J., Langereis M.A., Huizinga E.G., de Groot R.J. Coronavirus receptor switch explained from the stereochemistry of protein-carbohydrate interactions and a single mutation. Proc. Natl. Acad. Sci. U. S. A. 2016;113 [PMC free article] [PubMed] []
  • Barlan A., Zhao J., Sarkar M.K., Li K., McCray P.B., Perlman S., Gallagher T. Receptor variation and susceptibility to Middle East respiratory syndrome coronavirus infection. J. Virol. 2014;88:4953. [PMC free article] [PubMed] []
  • Belouzard S., Chu V.C., Whittaker G.R. Activation of the SARS coronavirus spike protein via sequential proteolytic cleavage at two distinct sites. Proc. Natl. Acad. Sci. U. S. A. 2009;106:5871. [PMC free article] [PubMed] []
  • Beniac D.R., Andonov A., Grudeski E., Booth T.F. Architecture of the SARS coronavirus prefusion spike. Nat. Struct. Mol. Biol. 2006;13:751. [PMC free article] [PubMed] []
  • Beniac D.R., deVarennes S.L., Andonov A., He R., Booth T.F. Conformational reorganization of the SARS coronavirus spike following receptor binding: implications for membrane fusion. PLoS One. 2007;2 [PMC free article] [PubMed] []
  • Bos E.C., Heijnen L., Spaan W.J. Site directed mutagenesis of the murine coronavirus spike protein. Effects on fusion. Adv. Exp. Med. Biol. 1995;380:283. [PubMed] []
  • Bosch B.J., Bartelink W., Rottier P.J. Cathepsin L functionally cleaves the severe acute respiratory syndrome coronavirus class I fusion protein upstream of rather than adjacent to the fusion peptide. J. Virol. 2008;82:8887. [PMC free article] [PubMed] []
  • Bosch B.J., de Haan C.A., Smits S.L., Rottier P.J. Spike protein assembly into the coronavirion: exploring the limits of its sequence requirements. Virology. 2005;334:306. [PMC free article] [PubMed] []
  • Bosch B.J., van der Zee R., de Haan C.A., Rottier P.J. The coronavirus spike protein is a class I virus fusion protein: structural and functional characterization of the fusion core complex. J. Virol. 2003;77:8801. [PMC free article] [PubMed] []
  • Brilot A.F., Chen J.Z., Cheng A., Pan J., Harrison S.C., Potter C.S., Carragher B., Henderson R., Grigorieff N. Beam-induced motion of vitrified specimen on holey carbon film. J. Struct. Biol. 2012;177:630. [PMC free article] [PubMed] []
  • Burkard C., Verheije M.H., Wicht O., van Kasteren S.I., van Kuppeveld F.J., Haagmans B.L., Pelkmans L., Rottier P.J., Bosch B.J., de Haan C.A. Coronavirus cell entry occurs through the endo-/lysosomal pathway in a proteolysis-dependent manner. PLoS Pathog. 2014;10 [PMC free article] [PubMed] []
  • Campbell M.G., Cheng A., Brilot A.F., Moeller A., Lyumkis D., Veesler D., Pan J., Harrison S.C., Potter C.S., Carragher B., Grigorieff N. Movies of ice-embedded particles enhance resolution in electron cryo-microscopy. Structure. 2012;20:1823. [PMC free article] [PubMed] []
  • Campbell M.G., Veesler D., Cheng A., Potter C.S., Carragher B. 2.8 Å resolution reconstruction of the Thermoplasma acidophilum 20S proteasome using cryo-electron microscopy. Elife. 2015;4 [PMC free article] [PubMed] []
  • Chang K.W., Sheng Y., Gombold J.L. Coronavirus-induced membrane fusion requires the cysteine-rich domain in the spike protein. Virology. 2000;269:212. [PMC free article] [PubMed] []
  • Chen J., Kovacs J.M., Peng H., Rits-Volloch S., Lu J., Park D., Zablowsky E., Seaman M.S., Chen B. HIV-1 envelope. Effect of the cytoplasmic domain on antigenic characteristics of HIV-1 envelope glycoprotein. Science. 2015;349:191. [PMC free article] [PubMed] []
  • Chen Y., Rajashankar K.R., Yang Y., Agnihothram S.S., Liu C., Lin Y.L., Baric R.S., Li F. Crystal structure of the receptor-binding domain from newly emerged Middle East respiratory syndrome coronavirus. J. Virol. 2013;87:10777. [PMC free article] [PubMed] []
  • Corti D., Voss J., Gamblin S.J., Codoni G., Macagno A., Jarrossay D., Vachieri S.G., Pinna D., Minola A., Vanzetta F., Silacci C., Fernandez-Rodriguez B.M., Agatic G., Bianchi S., Giacchetto-Sasselli I., Calder L., Sallusto F., Collins P., Haire L.F., Temperton N., Langedijk J.P., Skehel J.J., Lanzavecchia A. A neutralizing antibody selected from plasma cells that binds to group 1 and group 2 influenza A hemagglutinins. Science. 2011;333:850. [PubMed] []
  • Corti D., Zhao J., Pedotti M., Simonelli L., Agnihothram S., Fett C., Fernandez-Rodriguez B., Foglierini M., Agatic G., Vanzetta F., Gopal R., Langrish C.J., Barrett N.A., Sallusto F., Baric R.S., Varani L., Zambon M., Perlman S., Lanzavecchia A. Prophylactic and postexposure efficacy of a potent human monoclonal antibody against MERS coronavirus. Proc. Natl. Acad. Sci. U. S. A. 2015;112:10473. [PMC free article] [PubMed] []
  • Daniel C., Anderson R., Buchmeier M.J., Fleming J.O., Spaan W.J., Wege H., Talbot P.J. Identification of an immunodominant linear neutralization domain on the S2 portion of the murine coronavirus spike glycoprotein and evidence that it forms part of complex tridimensional structure. J. Virol. 1993;67:1185. [PMC free article] [PubMed] []
  • Delmas B., Gelfi J., L'Haridon R., Vogel L.K., Sjöström H., Norén O., Laude H. Aminopeptidase N is a major receptor for the entero-pathogenic coronavirus TGEV. Nature. 1992;357:417. [PMC free article] [PubMed] []
  • Delmas B., Gelfi J., Sjöström H., Noren O., Laude H. Further characterization of aminopeptidase-N as a receptor for coronaviruses. Adv. Exp. Med. Biol. 1993;342:293. [PubMed] []
  • Dev J., Park D., Fu Q., Chen J., Ha H.J., Ghantous F., Herrmann T., Chang W., Liu Z., Frey G., Seaman M.S., Chen B., Chou J.J. Structural basis for membrane anchoring of HIV-1 envelope spike. Science. 2016;353:172. [PMC free article] [PubMed] []
  • Du L., Tai W., Yang Y., Zhao G., Zhu Q., Sun S., Liu C., Tao X., Tseng C.K., Perlman S., Jiang S., Zhou Y., Li F. Introduction of neutralizing immunogenicity index to the rational design of MERS coronavirus subunit vaccines. Nat. Commun. 2016;7:13473. [PMC free article] [PubMed] []
  • Duquerroy S., Vigouroux A., Rottier P.J., Rey F.A., Bosch B.J. Central ions and lateral asparagine/glutamine zippers stabilize the post-fusion hairpin conformation of the SARS coronavirus spike glycoprotein. Virology. 2005;335:276. [PMC free article] [PubMed] []
  • Dveksler G.S., Pensiero M.N., Cardellichio C.B., Williams R.K., Jiang G.S., Holmes K.V., Dieffenbach C.W. Cloning of the mouse hepatitis virus (MHV) receptor: expression in human and hamster cell lines confers susceptibility to MHV. J. Virol. 1991;65:6881. [PMC free article] [PubMed] []
  • Earnest J.T., Hantak M.P., Li K., McCray P.B., Perlman S., Gallagher T. The tetraspanin CD9 facilitates MERS-coronavirus entry by scaffolding host cell receptors and proteases. PLoS Pathog. 2017;13 [PMC free article] [PubMed] []
  • Earnest J.T., Hantak M.P., Park J.E., Gallagher T. Coronavirus and influenza virus proteolytic priming takes place in tetraspanin-enriched membrane microdomains. J. Virol. 2015;89:6093. [PMC free article] [PubMed] []
  • Eifart P., Ludwig K., Bottcher C., de Haan C.A., Rottier P.J., Korte T., Herrmann A. Role of endocytosis and low pH in murine hepatitis virus strain A59 cell entry. J. Virol. 2007;81:10758. [PMC free article] [PubMed] []
  • Frana M.F., Behnke J.N., Sturman L.S., Holmes K.V. Proteolytic cleavage of the E2 glycoprotein of murine coronavirus: host-dependent differences in proteolytic cleavage and cell fusion. J. Virol. 1985;56:912. [PMC free article] [PubMed] []
  • Gao J., Lu G., Qi J., Li Y., Wu Y., Deng Y., Geng H., Li H., Wang Q., Xiao H., Tan W., Yan J., Gao G.F. Structure of the fusion core and inhibition of fusion by a heptad repeat peptide derived from the S protein of Middle East respiratory syndrome coronavirus. J. Virol. 2013;87:13134. [PMC free article] [PubMed] []
  • Ge X.Y., Li J.L., Yang X.L., Chmura A.A., Zhu G., Epstein J.H., Mazet J.K., Hu B., Zhang W., Peng C., Zhang Y.J., Luo C.M., Tan B., Wang N., Zhu Y., Crameri G., Zhang S.Y., Wang L.F., Daszak P., Shi Z.L. Isolation and characterization of a bat SARS-like coronavirus that uses the ACE2 receptor. Nature. 2013;503:535. [PMC free article] [PubMed] []
  • Gui M., Song W., Zhou H., Xu J., Chen S., Xiang Y., Wang X. Cryo-electron microscopy structures of the SARS-CoV spike glycoprotein reveal a prerequisite conformational state for receptor binding. Cell Res. 2017;27:119. [PMC free article] [PubMed] []
  • Haagmans B.L., Al Dhahiry S.H., Reusken C.B., Raj V.S., Galiano M., Myers R., Godeke G.J., Jonges M., Farag E., Diab A., Ghobashy H., Alhajri F., Al-Thani M., Al-Marri S.A., Al Romaihi H.E., Al Khal A., Bermingham A., Osterhaus A.D., AlHajri M.M., Koopmans M.P. Middle East respiratory syndrome coronavirus in dromedary camels: an outbreak investigation. Lancet Infect. Dis. 2014;14:140. [PMC free article] [PubMed] []
  • Harrison S.C. Viral membrane fusion. Nat. Struct. Mol. Biol. 2008;15:690. [PMC free article] [PubMed] []
  • Heald-Sargent T., Gallagher T. Ready, set, fuse! The coronavirus spike protein and acquisition of fusion competence. Viruses. 2012;4:557. [PMC free article] [PubMed] []
  • Hofmann H., Pyrc K., van der Hoek L., Geier M., Berkhout B., Pohlmann S. Human coronavirus NL63 employs the severe acute respiratory syndrome coronavirus receptor for cellular entry. Proc. Natl. Acad. Sci. U. S. A. 2005;102:7988. [PMC free article] [PubMed] []
  • Hu B., Zeng L.P., Yang X.L., Ge X.Y., Zhang W., Li B., Xie J.Z., Shen X.R., Zhang Y.Z., Wang N., Luo D.S., Zheng X.S., Wang M.N., Daszak P., Wang L.F., Cui J., Shi Z.L. Discovery of a rich gene pool of bat SARS-related coronaviruses provides new insights into the origin of SARS coronavirus. PLoS Pathog. 2017;13 [PMC free article] [PubMed] []
  • Hulswit R.J., de Haan C.A., Bosch B.J. Coronavirus spike protein and tropism changes. Adv. Virus Res. 2016;96:29. [PMC free article] [PubMed] []
  • Hulswit R.J.G., Lang Y., Bakkers M.J.G., Li W., Li Z., Schouten A., Ophorst B., van Kuppeveld F.J.M., Boons G.J., Bosch B.J., Huizinga E.G., de Groot R.J. Human coronaviruses OC43 and HKU1 bind to 9-O-acetylated sialic acids via a conserved receptor-binding site in spike protein domain A. Proc. Natl. Acad. Sci. U. S. A. 2019;116:2681. [PMC free article] [PubMed] []
  • Inoue Y., Tanaka N., Tanaka Y., Inoue S., Morita K., Zhuang M., Hattori T., Sugamura K. Clathrin-dependent entry of severe acute respiratory syndrome coronavirus into target cells expressing ACE2 with the cytoplasmic tail deleted. J. Virol. 2007;81:8722. [PMC free article] [PubMed] []
  • Isaacs D., Flowers D., Clarke J.R., Valman H.B., MacNaughton M.R. Epidemiology of coronavirus respiratory infections. Arch. Dis. Child. 1983;58:500. [PMC free article] [PubMed] []
  • Kirchdoerfer R.N., Cottrell C.A., Wang N., Pallesen J., Yassine H.M., Turner H.L., Corbett K.S., Graham B.S., McLellan J.S., Ward A.B. Pre-fusion structure of a human coronavirus spike protein. Nature. 2016;531:118. [PMC free article] [PubMed] []
  • Kirchdoerfer R.N., Wang N., Pallesen J., Wrapp D., Turner H.L., Cottrell C.A., Corbett K.S., Graham B.S., McLellan J.S., Ward A.B. Stabilized coronavirus spikes are resistant to conformational changes induced by receptor recognition or proteolysis. Sci. Rep. 2018;8:15701. [PMC free article] [PubMed] []
  • Kong R., Xu K., Zhou T., Acharya P., Lemmin T., Liu K., Ozorowski G., Soto C., Taft J.D., Bailer R.T., Cale E.M., Chen L., Choi C.W., Chuang G.Y., Doria-Rose N.A., Druz A., Georgiev I.S., Gorman J., Huang J., Joyce M.G., Louder M.K., Ma X., McKee K., O'Dell S., Pancera M., Yang Y., Blanchard S.C., Mothes W., Burton D.R., Koff W.C., Connors M., Ward A.B., Kwong P.D., Mascola J.R. Fusion peptide of HIV-1 as a site of vulnerability to neutralizing antibody. Science. 2016;352:828. [PMC free article] [PubMed] []
  • Krempl C., Schultze B., Herrler G. Analysis of cellular receptors for human coronavirus OC43. Adv. Exp. Med. Biol. 1995;380:371. [PubMed] []
  • Krempl C., Schultze B., Laude H., Herrler G. Point mutations in the S protein connect the sialic acid binding activity with the enteropathogenicity of transmissible gastroenteritis coronavirus. J. Virol. 1997;71:3285. [PMC free article] [PubMed] []
  • Krokhin O., Li Y., Andonov A., Feldmann H., Flick R., Jones S., Stroeher U., Bastien N., Dasuri K.V., Cheng K., Simonsen J.N., Perreault H., Wilkins J., Ens W., Plummer F., Standing K.G. Mass spectrometric characterization of proteins from the SARS virus: a preliminary report. Mol. Cell. Proteomics. 2003;2:346. [PubMed] []
  • Lang S., Xie J., Zhu X., Wu N.C., Lerner R.A., Wilson I.A. Antibody 27F3 broadly targets influenza A group 1 and 2 hemagglutinins through a further variation in VH1-69 antibody orientation on the HA stem. Cell Rep. 2017;20:2935. [PMC free article] [PubMed] []
  • Li F., Li W., Farzan M., Harrison S.C. Structure of SARS coronavirus spike receptor-binding domain complexed with receptor. Science. 2005;309:1864. [PubMed] []
  • Li W., Hulswit R.J.G., Kenney S.P., Widjaja I., Jung K., Alhamo M.A., van Dieren B., van Kuppeveld F.J.M., Saif L.J., Bosch B.J. Broad receptor engagement of an emerging global coronavirus may potentiate its diverse cross-species transmissibility. Proc. Natl. Acad. Sci. U. S. A. 2018;115 [PMC free article] [PubMed] []
  • Li W., Hulswit R.J.G., Widjaja I., Raj V.S., McBride R., Peng W., Widagdo W., Tortorici M.A., van Dieren B., Lang Y., van Lent J.W.M., Paulson J.C., de Haan C.A.M., de Groot R.J., van Kuppeveld F.J.M., Haagmans B.L., Bosch B.J. Identification of sialic acid-binding function for the Middle East respiratory syndrome coronavirus spike glycoprotein. Proc. Natl. Acad. Sci. U. S. A. 2017;114 [PMC free article] [PubMed] []
  • Li W., Moore M.J., Vasilieva N., Sui J., Wong S.K., Berne M.A., Somasundaran M., Sullivan J.L., Luzuriaga K., Greenough T.C., Choe H., Farzan M. Angiotensin-converting enzyme 2 is a functional receptor for the SARS coronavirus. Nature. 2003;426:450. [PMC free article] [PubMed] []
  • Li W., Wicht O., van Kuppeveld F.J., He Q., Rottier P.J., Bosch B.J. A single point mutation creating a furin cleavage site in the spike protein renders porcine epidemic diarrhea coronavirus trypsin independent for cell entry and fusion. J. Virol. 2015;89:8077. [PMC free article] [PubMed] []
  • Li W., Zhang C., Sui J., Kuhn J.H., Moore M.J., Luo S., Wong S.K., Huang I.C., Xu K., Vasilieva N., Murakami A., He Y., Marasco W.A., Guan Y., Choe H., Farzan M. Receptor and viral determinants of SARS-coronavirus adaptation to human ACE2. EMBO J. 2005;24:1634. [PMC free article] [PubMed] []
  • Li X., Mooney P., Zheng S., Booth C.R., Braunfeld M.B., Gubbens S., Agard D.A., Cheng Y. Electron counting and beam-induced motion correction enable near-atomic-resolution single-particle cryo-EM. Nat. Methods. 2013;10:584. [PMC free article] [PubMed] []
  • Liu C., Tang J., Ma Y., Liang X., Yang Y., Peng G., Qi Q., Jiang S., Li J., Du L., Li F. Receptor usage and cell entry of porcine epidemic diarrhea coronavirus. J. Virol. 2015;89:6121. [PMC free article] [PubMed] []
  • Lontok E., Corse E., Machamer C.E. Intracellular targeting signals contribute to localization of coronavirus spike proteins near the virus assembly site. J. Virol. 2004;78:5913. [PMC free article] [PubMed] []
  • Lu G., Hu Y., Wang Q., Qi J., Gao F., Li Y., Zhang Y., Zhang W., Yuan Y., Bao J., Zhang B., Shi Y., Yan J., Gao G.F. Molecular basis of binding between novel human coronavirus MERS-CoV and its receptor CD26. Nature. 2013;500:227. [PMC free article] [PubMed] []
  • McCoy L.E., van Gils M.J., Ozorowski G., Messmer T., Briney B., Voss J.E., Kulp D.W., Macauley M.S., Sok D., Pauthner M., Menis S., Cottrell C.A., Torres J.L., Hsueh J., Schief W.R., Wilson I.A., Ward A.B., Sanders R.W., Burton D.R. Holes in the glycan shield of the native HIV envelope are a target of trimer-elicited neutralizing antibodies. Cell Rep. 2016;16:2327. [PMC free article] [PubMed] []
  • McLellan J.S., Chen M., Leung S., Graepel K.W., Du X., Yang Y., Zhou T., Baxa U., Yasuda E., Beaumont T., Kumar A., Modjarrad K., Zheng Z., Zhao M., Xia N., Kwong P.D., Graham B.S. Structure of RSV fusion glycoprotein trimer bound to a prefusion-specific neutralizing antibody. Science. 2013;340:1113. [PMC free article] [PubMed] []
  • McLellan J.S., Yang Y., Graham B.S., Kwong P.D. Structure of respiratory syncytial virus fusion glycoprotein in the postfusion conformation reveals preservation of neutralizing epitopes. J. Virol. 2011;85:7788. [PMC free article] [PubMed] []
  • Menachery V.D., Yount B.L., Debbink K., Agnihothram S., Gralinski L.E., Plante J.A., Graham R.L., Scobey T., Ge X.Y., Donaldson E.F., Randell S.H., Lanzavecchia A., Marasco W.A., Shi Z.L., Baric R.S. A SARS-like cluster of circulating bat coronaviruses shows potential for human emergence. Nat. Med. 2015;21:1508. [PMC free article] [PubMed] []
  • Menachery V.D., Yount B.L., Sims A.C., Debbink K., Agnihothram S.S., Gralinski L.E., Graham R.L., Scobey T., Plante J.A., Royal S.R., Swanstrom J., Sheahan T.P., Pickles R.J., Corti D., Randell S.H., Lanzavecchia A., Marasco W.A., Baric R.S. SARS-like WIV1-CoV poised for human emergence. Proc. Natl. Acad. Sci. U. S. A. 2016;113:3048. [PMC free article] [PubMed] []
  • Milewska A., Zarebski M., Nowak P., Stozek K., Potempa J., Pyrc K. Human coronavirus NL63 utilizes heparan sulfate proteoglycans for attachment to target cells. J. Virol. 2014;88 [PMC free article] [PubMed] []
  • Millet J.K., Whittaker G.R. Host cell entry of Middle East respiratory syndrome coronavirus after two-step, furin-mediated activation of the spike protein. Proc. Natl. Acad. Sci. U. S. A. 2014;111 [PMC free article] [PubMed] []
  • Millet J.K., Whittaker G.R. Host cell proteases: critical determinants of coronavirus tropism and pathogenesis. Virus Res. 2015;202:120. [PMC free article] [PubMed] []
  • Ng M.L., Tan S.H., See E.E., Ooi E.E., Ling A.E. Proliferative growth of SARS coronavirus in Vero E6 cells. J. Gen. Virol. 2003;84:3291. [PubMed] []
  • Nomura R., Kiyota A., Suzaki E., Kataoka K., Ohe Y., Miyamoto K., Senda T., Fujimoto T. Human coronavirus 229E binds to CD13 in rafts and enters the cell through caveolae. J. Virol. 2004;78:8701. [PMC free article] [PubMed] []
  • Owczarek K., Szczepanski A., Milewska A., Baster Z., Rajfur Z., Sarna M., Pyrc K. Early events during human coronavirus OC43 entry to the cell. Sci. Rep. 2018;8:7124. [PMC free article] [PubMed] []
  • Pallesen J., Wang N., Corbett K.S., Wrapp D., Kirchdoerfer R.N., Turner H.L., Cottrell C.A., Becker M.M., Wang L., Shi W., Kong W.P., Andres E.L., Kettenbach A.N., Denison M.R., Chappell J.D., Graham B.S., Ward A.B., McLellan J.S. Immunogenicity and structures of a rationally designed prefusion MERS-CoV spike antigen. Proc. Natl. Acad. Sci. U. S. A. 2017;114:E7348. [PMC free article] [PubMed] []
  • Park J.E., Li K., Barlan A., Fehr A.R., Perlman S., McCray P.B., Gallagher T. Proteolytic processing of Middle East respiratory syndrome coronavirus spikes expands virus tropism. Proc. Natl. Acad. Sci. U. S. A. 2016;113 [PMC free article] [PubMed] []
  • Peng G., Sun D., Rajashankar K.R., Qian Z., Holmes K.V., Li F. Crystal structure of mouse coronavirus receptor-binding domain complexed with its murine receptor. Proc. Natl. Acad. Sci. U. S. A. 2011;108 [PMC free article] [PubMed] []
  • Peng G., Xu L., Lin Y.L., Chen L., Pasquarella J.R., Holmes K.V., Li F. Crystal structure of bovine coronavirus spike protein lectin domain. J. Biol. Chem. 2012;287 [PMC free article] [PubMed] []
  • Petit C.M., Melancon J.M., Chouljenko V.N., Colgrove R., Farzan M., Knipe D.M., Kousoulas K.G. Genetic analysis of the SARS-coronavirus spike glycoprotein functional domains involved in cell-surface expression and cell-to-cell fusion. Virology. 2005;341:215. [PMC free article] [PubMed] []
  • Prabakaran P., Gan J., Feng Y., Zhu Z., Choudhry V., Xiao X., Ji X., Dimitrov D.S. Structure of severe acute respiratory syndrome coronavirus receptor-binding domain complexed with neutralizing antibody. J. Biol. Chem. 2006;281 [PubMed] []
  • Punjani A., Rubinstein J.L., Fleet D.J., Brubaker M.A. cryoSPARC: algorithms for rapid unsupervised cryo-EM structure determination. Nat. Methods. 2017;14:290. [PubMed] []
  • Raj V.S., Mou H., Smits S.L., Dekkers D.H., Muller M.A., Dijkman R., Muth D., Demmers J.A., Zaki A., Fouchier R.A., Thiel V., Drosten C., Rottier P.J., Osterhaus A.D., Bosch B.J., Haagmans B.L. Dipeptidyl peptidase 4 is a functional receptor for the emerging human coronavirus-EMC. Nature. 2013;495:251. [PMC free article] [PubMed] []
  • Regan A.D., Shraybman R., Cohen R.D., Whittaker G.R. Differential role for low pH and cathepsin-mediated cleavage of the viral spike protein during entry of serotype II feline coronaviruses. Vet. Microbiol. 2008;132:235. [PMC free article] [PubMed] []
  • Reguera J., Santiago C., Mudgal G., Ordoño D., Enjuanes L., Casasnovas J.M. Structural bases of coronavirus attachment to host aminopeptidase N and its inhibition by neutralizing antibodies. PLoS Pathog. 2012;8 [PMC free article] [PubMed] []
  • Ritchie G., Harvey D.J., Feldmann F., Stroeher U., Feldmann H., Royle L., Dwek R.A., Rudd P.M. Identification of N-linked carbohydrates from severe acute respiratory syndrome (SARS) spike glycoprotein. Virology. 2010;399:257. [PMC free article] [PubMed] []
  • Rockx B., Corti D., Donaldson E., Sheahan T., Stadler K., Lanzavecchia A., Baric R. Structural basis for potent cross-neutralizing human monoclonal antibody protection against lethal human and zoonotic severe acute respiratory syndrome coronavirus challenge. J. Virol. 2008;82:3220. [PMC free article] [PubMed] []
  • Rosenthal P.B., Zhang X., Formanowski F., Fitz W., Wong C.H., Meier-Ewert H., Skehel J.J., Wiley D.C. Structure of the haemagglutinin-esterase-fusion glycoprotein of influenza C virus. Nature. 1998;396:92. [PMC free article] [PubMed] []
  • Sabir J.S., Lam T.T., Ahmed M.M., Li L., Shen Y., Abo-Aba S.E., Qureshi M.I., Abu-Zeid M., Zhang Y., Khiyami M.A., Alharbi N.S., Hajrah N.H., Sabir M.J., Mutwakil M.H., Kabli S.A., Alsulaimany F.A., Obaid A.Y., Zhou B., Smith D.K., Holmes E.C., Zhu H., Guan Y. Co-circulation of three camel coronavirus species and recombination of MERS-CoVs in Saudi Arabia. Science. 2016;351:81. [PubMed] []
  • Scheres S.H. RELION: implementation of a Bayesian approach to cryo-EM structure determination. J. Struct. Biol. 2012;180:519. [PMC free article] [PubMed] []
  • Schroth-Diez B., Ludwig K., Baljinnyam B., Kozerski C., Huang Q., Herrmann A. The role of the transmembrane and of the intraviral domain of glycoproteins in membrane fusion of enveloped viruses. Biosci. Rep. 2000;20:571. [PubMed] []
  • Schwegmann-Wessels C., Zimmer G., Schröder B., Breves G., Herrler G. Binding of transmissible gastroenteritis coronavirus to brush border membrane sialoglycoproteins. J. Virol. 2003;77 [PMC free article] [PubMed] []
  • Shang J., Zheng Y., Yang Y., Liu C., Geng Q., Luo C., Zhang W., Li F. Cryo-EM structure of infectious bronchitis coronavirus spike protein reveals structural and functional evolution of coronavirus spike proteins. PLoS Pathog. 2018;14 [PMC free article] [PubMed] []
  • Shang J., Zheng Y., Yang Y., Liu C., Geng Q., Tai W., Du L., Zhou Y., Zhang W., Li F. Cryo-electron microscopy structure of porcine deltacoronavirus spike protein in the prefusion state. J. Virol. 2018;92(4) pii: e01556-17. [PMC free article] [PubMed] []
  • Shulla A., Heald-Sargent T., Subramanya G., Zhao J., Perlman S., Gallagher T. A transmembrane serine protease is linked to the severe acute respiratory syndrome coronavirus receptor and activates virus entry. J. Virol. 2011;85:873. [PMC free article] [PubMed] []
  • Simmons G., Gosalia D.N., Rennekamp A.J., Reeves J.D., Diamond S.L., Bates P. Inhibitors of cathepsin L prevent severe acute respiratory syndrome coronavirus entry. Proc. Natl. Acad. Sci. U. S. A. 2005;102 [PMC free article] [PubMed] []
  • Song W., Gui M., Wang X., Xiang Y. Cryo-EM structure of the SARS coronavirus spike glycoprotein in complex with its host cell receptor ACE2. PLoS Pathog. 2018;14 [PMC free article] [PubMed] []
  • Stertz S., Reichelt M., Spiegel M., Kuri T., Martínez-Sobrido L., García-Sastre A., Weber F., Kochs G. The intracellular sites of early replication and budding of SARS-coronavirus. Virology. 2007;361:304. [PMC free article] [PubMed] []
  • Su S., Wong G., Shi W., Liu J., Lai A.C.K., Zhou J., Liu W., Bi Y., Gao G.F. Epidemiology, genetic recombination, and pathogenesis of coronaviruses. Trends Microbiol. 2016;24:490. [PMC free article] [PubMed] []
  • Supekar V.M., Bruckmann C., Ingallinella P., Bianchi E., Pessi A., Carfí A. Structure of a proteolytically resistant core from the severe acute respiratory syndrome coronavirus S2 fusion protein. Proc. Natl. Acad. Sci. U. S. A. 2004;101 [PMC free article] [PubMed] []
  • Swanson K., Wen X., Leser G.P., Paterson R.G., Lamb R.A., Jardetzky T.S. Structure of the Newcastle disease virus F protein in the post-fusion conformation. Virology. 2010;402:372. [PMC free article] [PubMed] []
  • Swanson K.A., Settembre E.C., Shaw C.A., Dey A.K., Rappuoli R., Mandl C.W., Dormitzer P.R., Carfi A. Structural basis for immunization with postfusion respiratory syncytial virus fusion F glycoprotein (RSV F) to elicit high neutralizing antibody titers. Proc. Natl. Acad. Sci. U. S. A. 2011;108:9619. [PMC free article] [PubMed] []
  • Thorp E.B., Boscarino J.A., Logan H.L., Goletz J.T., Gallagher T.M. Palmitoylations on murine coronavirus spike proteins are essential for virion assembly and infectivity. J. Virol. 2006;80:1280. [PMC free article] [PubMed] []
  • Tortorici M.A., Walls A.C., Lang Y., Wang C., Li Z., Koerhuis D., Boons G.J., Bosch B.J., Rey F.A., de Groot R.J., Veesler D. Structural basis for human coronavirus attachment to sialic acid receptors. Nat. Struct. Mol. Biol. 2019;26:481. [PMC free article] [PubMed] []
  • Traggiai E., Becker S., Subbarao K., Kolesnikova L., Uematsu Y., Gismondo M.R., Murphy B.R., Rappuoli R., Lanzavecchia A. An efficient method to make human monoclonal antibodies from memory B cells: potent neutralization of SARS coronavirus. Nat. Med. 2004;10:871. [PMC free article] [PubMed] []
  • Van Hamme E., Dewerchin H.L., Cornelissen E., Verhasselt B., Nauwynck H.J. Clathrin- and caveolae-independent entry of feline infectious peritonitis virus in monocytes depends on dynamin. J. Gen. Virol. 2008;89:2147. [PubMed] []
  • Vlasak R., Luytjes W., Spaan W., Palese P. Human and bovine coronaviruses recognize sialic acid-containing receptors similar to those of influenza C viruses. Proc. Natl. Acad. Sci. U. S. A. 1988;85:4526. [PMC free article] [PubMed] []
  • Walls A., Tortorici M.A., Bosch B.J., Frenz B., Rottier P.J., DiMaio F., Rey F.A., Veesler D. Crucial steps in the structure determination of a coronavirus spike glycoprotein using cryo-electron microscopy. Protein Sci. 2017;26:113. [PMC free article] [PubMed] []
  • Walls A.C., Tortorici M.A., Bosch B.J., Frenz B., Rottier P.J.M., DiMaio F., Rey F.A., Veesler D. Cryo-electron microscopy structure of a coronavirus spike glycoprotein trimer. Nature. 2016;531:114. [PMC free article] [PubMed] []
  • Walls A.C., Tortorici M.A., Frenz B., Snijder J., Li W., Rey F.A., DiMaio F., Bosch B.J., Veesler D. Glycan shield and epitope masking of a coronavirus spike protein observed by cryo-electron microscopy. Nat. Struct. Mol. Biol. 2016;23:899. [PMC free article] [PubMed] []
  • Walls A.C., Tortorici M.A., Snijder J., Xiong X., Bosch B.J., Rey F.A., Veesler D. Tectonic conformational changes of a coronavirus spike glycoprotein promote membrane fusion. Proc. Natl. Acad. Sci. U. S. A. 2017;114 [PMC free article] [PubMed] []
  • Walls A.C., Xiong X., Park Y.J., Tortorici M.A., Snijder J., Quispe J., Cameroni E., Gopal R., Dai M., Lanzavecchia A., Zambon M., Rey F.A., Corti D., Veesler D. Unexpected receptor functional mimicry elucidates activation of coronavirus fusion. Cell. 2019;176:1026. [PMC free article] [PubMed] []
  • Wang N., Shi X., Jiang L., Zhang S., Wang D., Tong P., Guo D., Fu L., Cui Y., Liu X., Arledge K.C., Chen Y.H., Zhang L., Wang X. Structure of MERS-CoV spike receptor-binding domain complexed with human receptor DPP4. Cell Res. 2013;23:986. [PMC free article] [PubMed] []
  • Wang Q., Qi J., Yuan Y., Xuan Y., Han P., Wan Y., Ji W., Li Y., Wu Y., Wang J., Iwamoto A., Woo P.C., Yuen K.Y., Yan J., Lu G., Gao G.F. Bat origins of MERS-CoV supported by bat coronavirus HKU4 usage of human receptor CD26. Cell Host Microbe. 2014;16:328. [PMC free article] [PubMed] []
  • Wang S., Guo F., Liu K., Wang H., Rao S., Yang P., Jiang C. Endocytosis of the receptor-binding domain of SARS-CoV spike protein together with virus receptor ACE2. Virus Res. 2008;136:8. [PMC free article] [PubMed] []
  • Wicht O., Li W., Willems L., Meuleman T.J., Wubbolts R.W., van Kuppeveld F.J., Rottier P.J., Bosch B.J. Proteolytic activation of the porcine epidemic diarrhea coronavirus spike fusion protein by trypsin in cell culture. J. Virol. 2014;88:7952. [PMC free article] [PubMed] []
  • Wickramasinghe I.N., de Vries R.P., Grone A., de Haan C.A., Verheije M.H. Binding of avian coronavirus spike proteins to host factors reflects virus tropism and pathogenicity. J. Virol. 2011;85:8903. [PMC free article] [PubMed] []
  • Williams R.K., Jiang G.S., Holmes K.V. Receptor for mouse hepatitis virus is a member of the carcinoembryonic antigen family of glycoproteins. Proc. Natl. Acad. Sci. U. S. A. 1991;88:5533. [PMC free article] [PubMed] []
  • Wong A.H.M., Tomlinson A.C.A., Zhou D., Satkunarajah M., Chen K., Sharon C., Desforges M., Talbot P.J., Rini J.M. Receptor-binding loops in alphacoronavirus adaptation and evolution. Nat. Commun. 2017;8:1735. [PMC free article] [PubMed] []
  • Wong J.J., Paterson R.G., Lamb R.A., Jardetzky T.S. Structure and stabilization of the Hendra virus F glycoprotein in its prefusion form. Proc. Natl. Acad. Sci. U. S. A. 2016;113:1056. [PMC free article] [PubMed] []
  • Wu K., Li W., Peng G., Li F. Crystal structure of NL63 respiratory coronavirus receptor-binding domain complexed with its human receptor. Proc. Natl. Acad. Sci. U. S. A. 2009;106 [PMC free article] [PubMed] []
  • Xiong X., Coombs P.J., Martin S.R., Liu J., Xiao H., McCauley J.W., Locher K., Walker P.A., Collins P.J., Kawaoka Y., Skehel J.J., Gamblin S.J. Receptor binding by a ferret-transmissible H5 avian influenza virus. Nature. 2013;497:392. [PubMed] []
  • Xiong X., Tortorici M.A., Snijder J., Yoshioka C., Walls A.C., Li W., McGuire A.T., Rey F.A., Bosch B.J., Veesler D. Glycan shield and fusion activation of a deltacoronavirus spike glycoprotein fine-tuned for enteric infections. J. Virol. 2018;92(4) pii: e01628-17. [PMC free article] [PubMed] []
  • Xu K., Chan Y.P., Bradel-Tretheway B., Akyol-Ataman Z., Zhu Y., Dutta S., Yan L., Feng Y., Wang L.F., Skiniotis G., Lee B., Zhou Z.H., Broder C.C., Aguilar H.C., Nikolov D.B. Crystal structure of the pre-fusion nipah virus fusion glycoprotein reveals a novel hexamer-of-trimers assembly. PLoS Pathog. 2015;11 [PMC free article] [PubMed] []
  • Xu Y., Liu Y., Lou Z., Qin L., Li X., Bai Z., Pang H., Tien P., Gao G.F., Rao Z. Structural basis for coronavirus-mediated membrane fusion. Crystal structure of mouse hepatitis virus spike protein fusion core. J. Biol. Chem. 2004;279 [PubMed] []
  • Xu Y., Su N., Qin L., Bai Z., Gao G.F., Rao Z. Crystallization and preliminary crystallographic analysis of the heptad-repeat complex of SARS coronavirus spike protein. Acta Crystallogr. D Biol. Crystallogr. 2004;60:2377. [PubMed] []
  • Yamada Y., Liu D.X. Proteolytic activation of the spike protein at a novel RRRR/S motif is implicated in furin-dependent entry, syncytium formation, and infectivity of coronavirus infectious bronchitis virus in cultured cells. J. Virol. 2009;83:8744. [PMC free article] [PubMed] []
  • Yang Y., Liu C., Du L., Jiang S., Shi Z., Baric R.S., Li F. Two mutations were critical for bat-to-human transmission of Middle East respiratory syndrome coronavirus. J. Virol. 2015;89:9119. [PMC free article] [PubMed] []
  • Ye R., Montalto-Morrison C., Masters P.S. Genetic analysis of determinants for spike glycoprotein assembly into murine coronavirus virions: distinct roles for charge-rich and cysteine-rich regions of the endodomain. J. Virol. 2004;78:9904. [PMC free article] [PubMed] []
  • Yeager C.L., Ashmun R.A., Williams R.K., Cardellichio C.B., Shapiro L.H., Look A.T., Holmes K.V. Human aminopeptidase N is a receptor for human coronavirus 229E. Nature. 1992;357:420. [PMC free article] [PubMed] []
  • Yin H.S., Paterson R.G., Wen X., Lamb R.A., Jardetzky T.S. Structure of the uncleaved ectodomain of the paramyxovirus (hPIV3) fusion protein. Proc. Natl. Acad. Sci. U. S. A. 2005;102:9288. [PMC free article] [PubMed] []
  • Yin H.S., Wen X., Paterson R.G., Lamb R.A., Jardetzky T.S. Structure of the parainfluenza virus 5 F protein in its metastable, prefusion conformation. Nature. 2006;439:38. [PMC free article] [PubMed] []
  • Youn S., Collisson E.W., Machamer C.E. Contribution of trafficking signals in the cytoplasmic tail of the infectious bronchitis virus spike protein to virus infection. J. Virol. 2005;79 [PMC free article] [PubMed] []
  • Yu X., Zhang S., Jiang L., Cui Y., Li D., Wang D., Wang N., Fu L., Shi X., Li Z., Zhang L., Wang X. Structural basis for the neutralization of MERS-CoV by a human monoclonal antibody MERS-27. Sci. Rep. 2015;5 [PMC free article] [PubMed] []
  • Yuan Y., Cao D., Zhang Y., Ma J., Qi J., Wang Q., Lu G., Wu Y., Yan J., Shi Y., Zhang X., Gao G.F. Cryo-EM structures of MERS-CoV and SARS-CoV spike glycoproteins reveal the dynamic receptor binding domains. Nat. Commun. 2017;8 [PMC free article] [PubMed] []
  • Zhang H., Wang G., Li J., Nie Y., Shi X., Lian G., Wang W., Yin X., Zhao Y., Qu X., Ding M., Deng H. Identification of an antigenic determinant on the S2 domain of the severe acute respiratory syndrome coronavirus spike glycoprotein capable of inducing neutralizing antibodies. J. Virol. 2004;78:6938. [PMC free article] [PubMed] []
  • Zheng Q., Deng Y., Liu J., van der Hoek L., Berkhout B., Lu M. Core structure of S2 from the human coronavirus NL63 spike glycoprotein. Biochemistry. 2006;45 [PubMed] []