The three known highly pathogenic human coronaviruses are severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Human highly pathogenic coronaviruses are composed of non-structural proteins, structural proteins, accessory proteins and ribonucleic acid. Viral particles recognize host receptors via spike glycoprotein (S protein), enter host cells by membrane fusion, replicate in host cells through large replication-transcription complexes, and promote proliferation by interfering with and suppressing the host's immune response. Highly pathogenic human coronaviruses are hosted by humans and vertebrates. Viral particles are transmitted through droplets, contact and aerosols or likely through digestive tract, urine, eyes and other routes. This review discusses the mechanisms of replication and transmission of highly pathogenic human coronaviruses providing basis for future studies on interrupting the transmission and pathogenicity of these pathogenic viruses.
Animals ; Betacoronavirus ; Coronavirus Infections ; Humans ; Middle East Respiratory Syndrome Coronavirus ; Pandemics ; Pneumonia, Viral ; Spike Glycoprotein, Coronavirus

Middle East respiratory syndrome (MERS) has raised global public health concerns. The recent outbreak of MERS coronavirus (MERS-CoV) infection has led to 1 338 laboratory-confirmed cases in 26 countries worldwide as reported till 19 June, 2015. MERS-CoV may be considered a zoonotic virus that has crossed the species barrier to humans, but the pathogenesis and the routes of transmission are not completely understood. Most MERS-CoV cases reported thus far have a history of residence in or travel to the Middle East. Human-to-human transmission though was observed on some occasions in Korea, it is documented as non-sustainable event. The envelope spike glycoprotein on the surface of MERS-CoV which mediates receptor binding, membrane fusion and viral entry is thought to be involved in the mechanism of MERS-CoV.No specific and effective treatment for MERS-CoV is currently recommended, although supportive treatment has played an important role. Prophylactic strategies are necessary to prevent MERS-CoV infection.
Coronavirus Infections ; diagnosis ; epidemiology ; therapy ; Humans ; Middle East Respiratory Syndrome Coronavirus ; pathogenicity ; physiology ; Spike Glycoprotein, Coronavirus ; metabolism ; Virus Internalization

Although the coronavirus disease 2019 (COVID-19) epidemic is still ongoing, vaccination rates are rising slowly and related treatments and drugs are being developed. At the same time, there is increasing evidence of preexisting immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in humans, mainly consisting of preexisting antibodies and immune cells (including T cells and B cells). The presence of these antibodies is mainly due to the seasonal prevalence of four common coronavirus types, especially OC43 and HKU1. The accumulated relevant evidence has suggested that the target of antibodies is mainly the S2 subunit of S protein, followed by evolutionary conservative regions such as the nucleocapsid (N) protein. Additionally, preexisting memory T and B cells are also present in the population. Preexisting antibodies can help the body protect against SARS-CoV-2 infection, reduce the severity of COVID-19, and rapidly increase the immune response post-infection. These multiple effects can directly affect disease progression and even the likelihood of death in certain individuals. Besides the positive effects, preexisting immunity may also have negative consequences, such as antibody-dependent enhancement (ADE) and original antigenic sin (OAS), the prevalence of which needs to be further established. In the future, more research should be focused on evaluating the role of preexisting immunity in COVID-19 outcomes, adopting appropriate policies and strategies for fighting the pandemic, and vaccine development that considers preexisting immunity.
COVID-19 ; Humans ; Pandemics ; SARS-CoV-2 ; Seasons ; Spike Glycoprotein, Coronavirus

OBJECTIVE: Late 2019 witnessed the outbreak and widespread transmission of coronavirus disease 2019 (COVID-19), a new, highly contagious disease caused by novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Consequently, considerable attention has been paid to the development of new diagnostic tools for the early detection of SARS-CoV-2. METHODS: In this study, a new poly-N-isopropylacrylamide microgel-based electrochemical sensor was explored to detect the SARS-CoV-2 spike protein (S protein) in human saliva. The microgel was composed of a copolymer of N-isopropylacrylamide and acrylic acid, and gold nanoparticles were encapsulated within the microgel through facile and economical fabrication. The electrochemical performance of the sensor was evaluated through differential pulse voltammetry. RESULTS: Under optimal experimental conditions, the linear range of the sensor was 10 ^-13-10 ^-9 mg/mL, whereas the detection limit was 9.55 fg/mL. Furthermore, the S protein was instilled in artificial saliva as the infected human saliva model, and the sensing platform showed satisfactory detection capability. CONCLUSION The sensing platform exhibited excellent specificity and sensitivity in detecting spike protein, indicating its potential application for the time-saving and inexpensive detection of SARS-CoV-2.
Humans ; Microgels ; Spike Glycoprotein, Coronavirus ; COVID-19/diagnosis* ; Gold ; Metal Nanoparticles ; SARS-CoV-2

Recently a COVID-19 pneumonia pandemic caused by a novel coronavirus 2019-nCoV has broken out over the world. In order to better control the spread of the pandemic, there's an urgent need to extensively study the virus' origin and the mechanisms for its infectivity and pathogenicity. Spike protein is a special structural protein on the surface of coronavirus. It contains important information about the evolution of the virus and plays critical roles in the processes of cellular recognition and entry. In the past decades, spike protein has always been one of the most important objects in research works on coronaviruses closely related to human life. In this review we introduce these research works related to spike proteins, hoping it will provide reasonable ideas for the control of the current pandemic, as well as for the diagnosis and treatment of COVID-19.
Betacoronavirus ; Coronavirus Infections ; diagnosis ; therapy ; Evolution, Molecular ; Humans ; Pandemics ; Pneumonia, Viral ; diagnosis ; therapy ; Spike Glycoprotein, Coronavirus ; analysis

The coronavirus disease 2019 (COVID-19) has caused global public health and economic crises. Thus, new therapeutic strategies and effective vaccines are urgently needed to cope with this severe pandemic. The development of a broadly neutralizing antibody against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is one of the attractive treatment strategies for COVID-19. Currently, the receptor-binding domain (RBD) of the spike (S) protein is the main target of neutralizing antibodies when SARS-CoV-2 enters human cells through an interaction between the S protein and the angiotensin-converting enzyme 2 expressed on various human cells. A single monoclonal antibody (mAb) treatment is prone to selective pressure due to increased possibility of targeted epitope mutation, leading to viral escape. In addition, the antibody-dependent enhancement effect is a potential risk of enhancing the viral infection. These risks can be reduced using multiple mAbs that target nonoverlapping epitopes. Thus, a cocktail therapy combining two or more antibodies that recognize different regions of the viral surface may be the most effective therapeutic strategy.
Antibodies, Monoclonal/therapeutic use* ; Antibodies, Neutralizing ; Antibodies, Viral ; COVID-19 ; Humans ; SARS-CoV-2 ; Spike Glycoprotein, Coronavirus

New threats posed by the emerging circulating variants of SARS-CoV-2 highlight the need to find conserved neutralizing epitopes for therapeutic antibodies and efficient vaccine design. Here, we identified a receptor-binding domain (RBD)-binding antibody, XG014, which potently neutralizes β-coronavirus lineage B (β-CoV-B), including SARS-CoV-2, its circulating variants, SARS-CoV and bat SARSr-CoV WIV1. Interestingly, antibody family members competing with XG014 binding show reduced levels of cross-reactivity and induce antibody-dependent SARS-CoV-2 spike (S) protein-mediated cell-cell fusion, suggesting a unique mode of recognition by XG014. Structural analyses reveal that XG014 recognizes a conserved epitope outside the ACE2 binding site and completely locks RBD in the non-functional "down" conformation, while its family member XG005 directly competes with ACE2 binding and position the RBD "up". Single administration of XG014 is effective in protection against and therapy of SARS-CoV-2 infection in vivo. Our findings suggest the potential to develop XG014 as pan-β-CoV-B therapeutics and the importance of the XG014 conserved antigenic epitope for designing broadly protective vaccines against β-CoV-B and newly emerging SARS-CoV-2 variants of concern.
Angiotensin-Converting Enzyme 2 ; Antibodies, Neutralizing ; Antibodies, Viral ; COVID-19 ; Epitopes ; Humans ; SARS-CoV-2/genetics* ; Spike Glycoprotein, Coronavirus/genetics*

OBJECTIVE: To explore the natural mutations in Spike protein (S protein) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the changes of affinity between virus and associated receptors or drug molecules before and after the mutation based on whole length sequencing results. METHODS: In the study, the bioinformatics analysis of all the published sequences of SARS-CoV-2 was conducted and thus the high frequency mutation sites were affirmed. Taking advantages of PolyPhen-2, the functional influence of each mutation in S protein was prospected. The 3D homologous modelling was performed by SWISS-MODEL to establish mutated S protein structural model, in which the protein-docking was then implemented with angiotensin-converting enzyme 2 (ACE2), dipeptidyl peptidase-4 (DPP4) and aminopeptidase N (APN) by ZDOCK, and the combining capacity of each mutated S protein evaluated by FiPD. Finally, the binding ability between mutated S proteins and anti-virus drugs were prospected and evaluated through AutoDock-Chimera 1.14. RESULTS: The mutations in specific region of S protein had greater tendency to destroy the S protein function by analysis of mutated S protein structure. Protein-receptor docking analysis between naturally mutated S protein and host receptors showed that, in the case of spontaneous mutation, the binding ability of S protein to ACE2 tended to be weakened, while the binding ability of DPP4 tended to be enhanced, and there was no significant change in the binding ability of APN. According to the computational simulation results of affinity binding between small molecular drugs and S protein, the affinity of aplaviroc with S protein was significantly higher than that of other small molecule drug candidates. CONCLUSION The region from 400-1 100 amino acid in S protein of SARS-CoV-2 is the mutation sensitive part during natural state, which was more potential to mutate than other part in S protein during natural state. The mutated SARS-CoV-2 might tend to target human cells with DPP4 as a new receptor rather than keep ACE2 as its unique receptor for human infection. At the same time, aplaviroc, which was used for the treatment of human immunodeficiency virus (HIV) infection, may become a new promising treatment for SARS-CoV-2 and could be a potential choice for the development of SARS-CoV-2 drugs.
Antiviral Agents ; COVID-19 ; Humans ; Peptidyl-Dipeptidase A/genetics* ; Point Mutation ; SARS-CoV-2 ; Spike Glycoprotein, Coronavirus/genetics*

OBJECTIVE: To provide data support for the study of pathogenic mechanism of SARS-CoV-2 at the molecular level, and provide suitable candidate targets for vaccine, antibody and drug research and development through comparative analysis for structural characteristics and epitopes of S protein of SARS-CoV-2 and SARS-CoV. METHODS: Based on the reference sequences of S protein, physical and chemical properties, hydrophobicity, signal peptide, transmembrane region, domain, secondary structure, tertiary structure analysis and antigenic epitopes prediction were carried out. Meanwhile, the tissue expression, related pathways and reactome pathways of angiotensis Ⅰ converting enzyme 2 (ACE2) and C-type lectin domain family 4 member M (CLEC4M) receptors were analyzed. RESULTS: The amino acid sequence of S protein of SARS-CoV-2 and SARS-CoV has a 75.80% consistency. The structural characteristics of the two coronaviruses are highly consistent, but the secondary structure and tertiary structure of SARS-CoV-2 is not as obvious as SARS-CoV. ACE2 and CLEC4M are expressed in alimentary system, heart, kidney, lung and placenta. The main related the pathways of renin-angiotensin system, protein digestion and absorption pathway, and the reactome pathways of metabolism of angiotensinogen to angiotensins, GPCR ligand binding, are related to typical symptoms of coronavirus disease 2019 induced by SARS-CoV-2. Three pairs of highly or completely homologous epitopes of S protein were obtained. The 600-605, 695-703 and 888-896 amino acid residues in SARS-CoV-2 were highly homologous with 586-591, 677-685 and 870-878 amino acid residues in SARS-CoV, respectively. CONCLUSIONS The similarity of S protein of SARS-CoV-2 and SARS-CoV determines that they have similar infection patterns and clinical manifestations. The candidate epitopes with high reliability can provide reference for virus diagnosis and vaccine development.
Betacoronavirus ; Cell Adhesion Molecules ; Coronavirus Infections ; Epitopes ; Humans ; Lectins, C-Type ; Ligands ; Pandemics ; Peptidyl-Dipeptidase A ; Pneumonia, Viral ; Receptors, Cell Surface ; Receptors, Virus ; Reproducibility of Results ; Spike Glycoprotein, Coronavirus

Chloroplast-based expression system is promising for the hyper-expression of plant-derived recombinant therapeutic proteins and vaccines. To verify the feasibility of obtaining high-level expression of the SARS subunit vaccine and to provide a suitable plant-derived vaccine production platform against the severe acute respiratory syndrome coronavirus (SARS-CoV), a 193-amino acid fragment of SARS CoV spike protein receptor-binding domain (RBD), fused with the peptide vector cholera toxin B subunit (CTB), was expressed in tobacco chloroplasts. Codon-optimized CTB-RBD sequence was integrated into the chloroplast genome and homoplasmy was obtained, as confirmed by PCR and Southern blot analysis. Western blot showed expression of the recombinant fusion protein mostly in soluble monomeric form. Quantification of the recombinant fusion protein CTB-RBD was conducted by ELISA analysis from the transplastomic leaves at different developmental stages, attachment positions and time points in a day and the different expression levels of the CTB-RBD were observed with the highest expression of 10.2% total soluble protein obtained from mature transplastomic leaves. Taken together, our results demonstrate the feasibility of highly expressing SARS subunit vaccine RBD, indicating its potential in subsequent development of a plant-derived recombinant subunit vaccine and reagents production for antibody detection in SARS serological tests.
Chloroplasts ; metabolism ; Cholera Toxin ; Protein Interaction Domains and Motifs ; Recombinant Fusion Proteins ; biosynthesis ; SARS Virus ; Spike Glycoprotein, Coronavirus ; biosynthesis ; Tobacco ; metabolism ; Vaccines, Subunit ; biosynthesis