Human Severe Acute Respiratory Syndrome Coronavirus Research Articles

Epidemiology and Genomic Characterization of Two Novel SARS-Related Coronaviruses in Horseshoe Bats from Guangdong, China.

ABSTRACTSevere acute respiratory syndrome (SARS) coronavirus (SARS-CoV) and SARS-CoV-2, the causative agents of SARS, which broke out in 2003, and coronavirus disease 2019 (COVID-2019), which broke out in 2019, probably originated in Rhinolophus sinicus and R. affinis, respectively. Rhinolophus bats are important hosts for coronaviruses. Many SARS-related coronaviruses (SARSr-CoVs) have been detected in bats from different areas of China; however, the diversity of bat SARSr-CoVs is increasing, and their transmission mechanisms have attracted much attention. Here, we report the findings of SARSr-CoVs in R. sinicus and R. affinis from South China from 2008 to 2021. The full-length genome sequences of the two novel SARSr-CoVs obtained from Guangdong shared 83 to 88% and 71 to 72% nucleotide identities with human SARS-CoV and SARS-CoV-2, respectively, while sharing high similarity with human SARS-CoV in hypervariable open reading frame 8 (ORF8). Significant recombination occurred between the two novel SARSr-CoVs. Phylogenetic analysis showed that the two novel bat SARSr-CoVs from Guangdong were more distant than the bat SARSr-CoVs from Yunnan to human SARS-CoV. We found that transmission in bats contributes more to virus diversity than time. Although our results of the sequence analysis of the receptor-binding motif (RBM) and the expression pattern of angiotensin-converting enzyme 2 (ACE2) inferred that these viruses could not directly infect humans, risks still exist after some unpredictable mutations. Thus, this study increased our understanding of the genetic diversity and transmission of SARSr-CoVs carried by bats in the field.

Development a novel multiepitope DNA vaccine against human SARS coronavirus-2: an immunoinformatic designing study.

Human SARS coronavirus 2 (SARS-CoV-2) causes the current global COVID-19 pandemic. The production of an efficient vaccine against COVID-19 is under heavy investigation. In this study, we have designed a novel multiepitope DNA vaccine against SARS-CoV-2 using reverse vaccinology and DNA vaccine approaches. Applying these strategies led to reduce the time and costs of vaccine development and also improve the immune protective characteristics of the vaccine. For this purpose, epitopes of nucleocapsid, membrane glycoprotein, and ORF8 proteins of SARS-CoV-2 chose as targets for B and T-cell receptors. Accordingly, DNA sequences of selected epitopes have optimized for protein expression in the eukaryotic system. To this end, the Kozak and tissue plasminogen activator sequences were added into the epitope sequences for proper protein expression and secretion, respectively. Furthermore, interleukin-2 and beta-defensin 1 preproprotein sequences were incorporated to the designed DNA vaccine as an adjuvant. Modeling and refinement of fused protein composed of SARS-CoV-2 multiepitope antigens (fuspMA) have performed based on homology modeling of orthologous peptides, then constructed 3D model of fuspMA was more investigated during 50 ns of molecular dynamics simulation. Further bioinformatics predictions demonstrated that fuspMA is a stable protein with acceptable antigenic features and no allergenicity or toxicity characteristics. Finally, the affinity of fuspMA to the MHC I and II and TLRs molecules validated by the molecular docking procedure. In conclusion, it seems the designed multiepitope DNA vaccine could have a chance to be introduced as an efficient vaccine against COVID-19 after more in vivo evaluations.

Recent endemic coronavirus infection is associated with less-severe COVID-19.

Four different endemic coronaviruses (eCoVs) are etiologic agents for the seasonal common cold, and these eCoVs share extensive sequence homology with human SARS coronavirus 2 (SARS-CoV-2). Here, we show that individuals with, as compared with those without, a recent documented infection with eCoV were tested at greater frequency for respiratory infections but had a similar rate of SARS-CoV-2 acquisition. Importantly, the patients with a previously detected eCoV had less-severe coronavirus disease 2019 (COVID-19) illness. Our observations suggest that preexisting immune responses against endemic human coronaviruses can mitigate disease manifestations from SARS-CoV-2 infection.

Behavioral manipulation-key to the successful global spread of the new coronavirus SARS-CoV-2?

Human‐severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) interaction can have an array of various outcomes—it could be mortal, morbid or merely carrying minor health consequences. The very rapid global spread has raised the issue whether there are further multi‐dimensional consequences of SARS‐CoV‐2 infection on human behavior, the key of its transmission. During the coronavirus crisis, odd, abnormal, and irresponsible behavior has been reported in coronavirus disease 2019 (COVID‐19) individuals, particularly in super‐spreaders, that is, persons with a high viral load, thus constituting also super‐emitters. Indeed, cases of infected persons ignoring self‐confinement orders, intentionally disregarding physical distancing and multiplying social interactions, or even deliberately sneezing, spitting or coughing were reported. While it is known that some other viruses, such as rabies and even influenza do change human behavior, this remains unclear for SARS‐CoV‐2. In this perspective, we highlight the possibility that COVID‐19 is facilitated by altered human social behavior that benefits SARS‐CoV‐2 transmission, through showcasing similar virus‐induced changed behavior by other pathogens and relating this to reports from the gray literature.

Evolutionary Arms Race between Virus and Host Drives Genetic Diversity in Bat Severe Acute Respiratory Syndrome-Related Coronavirus Spike Genes.

The Chinese horseshoe bat (Rhinolophus sinicus), reservoir host of severe acute respiratory syndrome coronavirus (SARS-CoV), carries many bat SARS-related CoVs (SARSr-CoVs) with high genetic diversity, particularly in the spike gene. Despite these variations, some bat SARSr-CoVs can utilize the orthologs of the human SARS-CoV receptor, angiotensin-converting enzyme 2 (ACE2), for entry. It is speculated that the interaction between bat ACE2 and SARSr-CoV spike proteins drives diversity. Here, we identified a series of R. sinicus ACE2 variants with some polymorphic sites involved in the interaction with the SARS-CoV spike protein. Pseudoviruses or SARSr-CoVs carrying different spike proteins showed different infection efficiencies in cells transiently expressing bat ACE2 variants. Consistent results were observed by binding affinity assays between SARS-CoV and SARSr-CoV spike proteins and receptor molecules from bats and humans. All tested bat SARSr-CoV spike proteins had a higher binding affinity to human ACE2 than to bat ACE2, although they showed a 10-fold lower binding affinity to human ACE2 compared with that of their SARS-CoV counterpart. Structure modeling revealed that the difference in binding affinity between spike and ACE2 might be caused by the alteration of some key residues in the interface of these two molecules. Molecular evolution analysis indicates that some key residues were under positive selection. These results suggest that the SARSr-CoV spike protein and R. sinicus ACE2 may have coevolved over time and experienced selection pressure from each other, triggering the evolutionary arms race dynamics.IMPORTANCE Evolutionary arms race dynamics shape the diversity of viruses and their receptors. Identification of key residues which are involved in interspecies transmission is important to predict potential pathogen spillover from wildlife to humans. Previously, we have identified genetically diverse SARSr-CoVs in Chinese horseshoe bats. Here, we show the highly polymorphic ACE2 in Chinese horseshoe bat populations. These ACE2 variants support SARS-CoV and SARSr-CoV infection but with different binding affinities to different spike proteins. The higher binding affinity of SARSr-CoV spike to human ACE2 suggests that these viruses have the capacity for spillover to humans. The positive selection of residues at the interface between ACE2 and SARSr-CoV spike protein suggests long-term and ongoing coevolutionary dynamics between them. Continued surveillance of this group of viruses in bats is necessary for the prevention of the next SARS-like disease.

The Global Emergency of Novel Coronavirus (SARS-CoV-2): An Update of the Current Status and Forecasting.

Over the past two decades, there have been two major outbreaks where the crossover of animal Betacoronaviruses to humans has resulted in severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV). In December 2019, a global public health concern started with the emergence of a new strain of coronavirus (SARS-CoV-2 or 2019 novel coronavirus, 2019-nCoV) which has rapidly spread all over the world from its origin in Wuhan, China. SARS-CoV-2 belongs to the Betacoronavirus genus, which includes human SARS-CoV, MERS and two other human coronaviruses (HCoVs), HCoV-OC43 and HCoV-HKU1. The fatality rate of SARS-CoV-2 is lower than the two previous coronavirus epidemics, but it is faster spreading and the large number of infected people with severe viral pneumonia and respiratory illness, showed SARS-CoV-2 to be highly contagious. Based on the current published evidence, herein we summarize the origin, genetics, epidemiology, clinical manifestations, preventions, diagnosis and up to date treatments of SARS-CoV-2 infections in comparison with those caused by SARS-CoV and MERS-CoV. Moreover, the possible impact of weather conditions on the transmission of SARS-CoV-2 is also discussed. Therefore, the aim of the present review is to reconsider the two previous pandemics and provide a reference for future studies as well as therapeutic approaches.

Cross-neutralization of SARS-CoV-2 by a human monoclonal SARS-CoV antibody.

Severe acute respiratory syndrome coronavirus2 (SARS-CoV-2) is a newly emerged coronavirus that is responsible for the current pandemic of coronavirus disease 2019 (COVID-19), which has resulted in more than 3.7million infections and 260,000deaths as of 6May 20201,2. Vaccine and therapeutic discovery efforts are paramount to curb the pandemic spread of this zoonotic virus. The SARS-CoV-2 spike (S) glycoprotein promotes entry into host cells and is the main target of neutralizing antibodies. Here we describe several monoclonal antibodies that target the Sglycoprotein of SARS-CoV-2, which we identified from memory Bcells of an individual who was infected with severe acute respiratory syndrome coronavirus (SARS-CoV) in 2003. One antibody (named S309) potently neutralizes SARS-CoV-2 and SARS-CoV pseudoviruses as well as authentic SARS-CoV-2, by engaging the receptor-binding domain of the Sglycoprotein. Using cryo-electron microscopy and binding assays, we show that S309 recognizes an epitope containing a glycan that is conserved within the Sarbecovirus subgenus, without competing with receptor attachment. Antibody cocktails that include S309 in combination with other antibodies that we identified further enhanced SARS-CoV-2 neutralization, and may limit the emergence of neutralization-escape mutants. These results pave the way for using S309 and antibody cocktails containing S309 for prophylaxis in individuals at a high risk of exposure or as a post-exposure therapy to limit or treat severe disease.

Genomic and protein structure modelling analysis depicts the origin and pathogenicity of 2019-nCoV, a new coronavirus which caused a pneumonia outbreak in Wuhan, China

Background: A pandemic outbreak caused by a novel coronavirus, 2019-nCoV, has originated from Wuhan, China and spread to many countries around the world. The outbreak has led to around 45 thousand cases and over one thousand death so far. Methods: Phylogenetic analysis and sequence alignment were used to align the whole genome sequence of 2019-nCoV with other over 200 sequences of coronaviruses to predict the origin of this novel virus. In addition, protein modeling and analysis were performed to access the potential binding of the spike protein of 2019-nCoV with human cell receptor, angiotensin-converting enzyme 2 (ACE2). Results: Detailed genomic and structure-based analysis of a new coronavirus, namely 2019-nCoV, showed that the new virus is a new type of bat coronavirus and is genetically fairly distant from the human SARS coronavirus. Structure analysis of the spike (S) protein of this new virus showed that its S protein only binds much weaker to the ACE2 receptor on human cells whereas the human SARS coronavirus exhibits strongly affinity to the ACE receptor. Conclusions: These findings suggest that the new virus should theoretically not be able to cause very serious human infection when compared to human SARS virus. However, the lower pathogenicity of this new virus may lead to longer incubation time and better adaption to human, which may favor its efficient transmission in human. These data are important to guide design of infection control policy and inform the public on the nature of threat imposed by 2019-nCov. Most importantly, using the analysis platform that we have developed, we should be able to predict whether the new mutations could lead to the increase of infectivity of the mutated virus in a very short time.

Discovery of a rich gene pool of bat SARS-related coronaviruses provides new insights into the origin of SARS coronavirus.

A large number of SARS-related coronaviruses (SARSr-CoV) have been detected in horseshoe bats since 2005 in different areas of China. However, these bat SARSr-CoVs show sequence differences from SARS coronavirus (SARS-CoV) in different genes (S, ORF8, ORF3, etc) and are considered unlikely to represent the direct progenitor of SARS-CoV. Herein, we report the findings of our 5-year surveillance of SARSr-CoVs in a cave inhabited by multiple species of horseshoe bats in Yunnan Province, China. The full-length genomes of 11 newly discovered SARSr-CoV strains, together with our previous findings, reveals that the SARSr-CoVs circulating in this single location are highly diverse in the S gene, ORF3 and ORF8. Importantly, strains with high genetic similarity to SARS-CoV in the hypervariable N-terminal domain (NTD) and receptor-binding domain (RBD) of the S1 gene, the ORF3 and ORF8 region, respectively, were all discovered in this cave. In addition, we report the first discovery of bat SARSr-CoVs highly similar to human SARS-CoV in ORF3b and in the split ORF8a and 8b. Moreover, SARSr-CoV strains from this cave were more closely related to SARS-CoV in the non-structural protein genes ORF1a and 1b compared with those detected elsewhere. Recombination analysis shows evidence of frequent recombination events within the S gene and around the ORF8 between these SARSr-CoVs. We hypothesize that the direct progenitor of SARS-CoV may have originated after sequential recombination events between the precursors of these SARSr-CoVs. Cell entry studies demonstrated that three newly identified SARSr-CoVs with different S protein sequences are all able to use human ACE2 as the receptor, further exhibiting the close relationship between strains in this cave and SARS-CoV. This work provides new insights into the origin and evolution of SARS-CoV and highlights the necessity of preparedness for future emergence of SARS-like diseases.

Effects of human anti-spike protein receptor binding domain antibodies on severe acute respiratory syndrome coronavirus neutralization escape and fitness.

The receptor binding domain (RBD) of the spike (S) glycoprotein of severe acute respiratory syndrome coronavirus (SARS-CoV) is a major target of protective immunity in vivo. Although a large number of neutralizing antibodies (nAbs) have been developed, it remains unclear if a single RBD-targeting nAb or two in combination can prevent neutralization escape and, if not, attenuate viral virulence in vivo. In this study, we used a large panel of human nAbs against an epitope that overlaps the interface between the RBD and its receptor, angiotensin-converting enzyme 2 (ACE2), to assess their cross-neutralization activities against a panel of human and zoonotic SARS-CoVs and neutralization escape mutants. We also investigated the neutralization escape profiles of these nAbs and evaluated their effects on receptor binding and virus fitness in vitro and in mice. We found that some nAbs had great potency and breadth in neutralizing multiple viral strains, including neutralization escape viruses derived from other nAbs; however, no single nAb or combination of two blocked neutralization escape. Interestingly, in mice the neutralization escape mutant viruses showed either attenuation (Urbani background) or increased virulence (GD03 background) consistent with the different binding affinities between their RBDs and the mouse ACE2. We conclude that using either single nAbs or dual nAb combinations to target a SARS-CoV RBD epitope that shows plasticity may have limitations for preventing neutralization escape during in vivo immunotherapy. However, RBD-directed nAbs may be useful for providing broad neutralization and prevention of escape variants when combined with other nAbs that target a second conserved epitope with less plasticity and more structural constraint. The emergence of severe acute respiratory syndrome coronavirus (SARS-CoV) in 2002 and Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012 has resulted in severe human respiratory disease with high death rates. Their zoonotic origins highlight the likelihood of reemergence or further evolution into novel human coronavirus pathogens. Broadly neutralizing antibodies (nAbs) that prevent infection of related viruses represent an important immunostrategy for combating coronavirus infections; however, for this strategy to succeed, it is essential to uncover nAb-mediated escape pathways and to pioneer strategies that prevent escape. Here, we used SARS-CoV as a research model and examined the escape pathways of broad nAbs that target the receptor binding domain (RBD) of the virus. We found that neither single nAbs nor two nAbs in combination blocked escape. Our results suggest that targeting conserved regions with less plasticity and more structural constraint rather than the SARS-CoV RBD-like region(s) should have broader utility for antibody-based immunotherapy.

Substitution at aspartic acid 1128 in the SARS coronavirus spike glycoprotein mediates escape from a S2 domain-targeting neutralizing monoclonal antibody.

The Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) is the etiological agent for the infectious disease, SARS, which first emerged 10 years ago. SARS-CoV is a zoonotic virus that has crossed the species barriers to infect humans. Bats, which harbour a diverse pool of SARS-like CoVs (SL-CoVs), are believed to be the natural reservoir. The SARS-CoV surface Spike (S) protein is a major antigenic determinant in eliciting neutralizing antibody production during SARS-CoV infection. In our previous work, we showed that a panel of murine monoclonal antibodies (mAbs) that target the S2 subunit of the S protein are capable of neutralizing SARS-CoV infection in vitro (Lip KM et al, J Virol. 2006 Jan; 80(2): 941–50). In this study, we report our findings on the characterization of one of these mAbs, known as 1A9, which binds to the S protein at a novel epitope within the S2 subunit at amino acids 1111–1130. MAb 1A9 is a broadly neutralizing mAb that prevents viral entry mediated by the S proteins of human and civet SARS-CoVs as well as bat SL-CoVs. By generating mutant SARS-CoV that escapes the neutralization by mAb 1A9, the residue D1128 in S was found to be crucial for its interaction with mAb 1A9. S protein containing the substitution of D1128 with alanine (D1128A) exhibited a significant decrease in binding capability to mAb 1A9 compared to wild-type S protein. By using a pseudotyped viral entry assay, it was shown that the D1128A substitution in the escape virus allows it to overcome the viral entry blockage by mAb 1A9. In addition, the D1128A mutation was found to exert no effects on the S protein cell surface expression and incorporation into virion particles, suggesting that the escape virus retains the same viral entry property as the wild-type virus.

Proteolytic processing, deubiquitinase and interferon antagonist activities of Middle East respiratory syndrome coronavirus papain-like protease

The emerging Middle East respiratory syndrome coronavirus (MERS-CoV) causes severe pulmonary disease in humans and represents the second example of a highly pathogenic coronavirus (CoV) following severe acute respiratory syndrome coronavirus (SARS-CoV). Genomic studies revealed that two viral proteases, papain-like protease (PLpro) and 3C-like protease (3CLpro), process the polyproteins encoded by the MERS-CoV genomic RNA. We previously reported that SARS-CoV PLpro acts as both deubiquitinase (DUB) and IFN antagonist, but the function of the MERS-CoV PLpro was poorly understood. In this study, we characterized MERS-CoV PLpro, which is a protease and can recognize and process the cleavage sites (CS) of nsp1-2, nsp2-3 and nsp3-4. The LXGG consensus cleavage sites in the N terminus of pp1a/1ab, which is generally essential for CoV PLpro-mediated processing, were also characterized in MERS-CoV. MERS-CoV PLpro, like human SARS-CoV PLpro and NL63-CoV PLP2, is a viral deubiquitinating enzyme. It acts on both K48- and K63-linked ubiquitination and ISG15-linked ISGylation. We confirmed that MERS-CoV PLpro acts as an IFN antagonist through blocking the phosphorylation and nuclear translocation of IFN regulatory factor 3 (IRF3). These findings indicate that MERS-CoV PLpro acts as a viral DUB and suppresses production of IFN-β by an interfering IRF3-mediated signalling pathway, in addition to recognizing and processing the CS at the N terminus of replicase polyprotein to release the non-structural proteins. The characterization of proteolytic processing, DUB and IFN antagonist activities of MERS-CoV PLpro would reveal the interactions between MERS-CoV and its host, and be applicable to develop strategies targeting PLpro for the effective control of MERS-CoV infection.

SARS-CoV ancestor found in Chinese bats

A new study reports the isolation of a novel coronavirus (CoV) from Chinese horseshoe bats, which is more closely related to severe acute respiratory syndrome coronavirus (SARS-CoV) than any previously identified bat CoV, providing strong evidence that SARS-CoV might have originated in bats. Whole-genome sequencing of the novel CoV revealed that it shares 95% sequence identity with human SARS-CoV, with the receptor-binding domain (RBD) in the spike protein from both viruses showing an identical amino acid sequence. The RBD of human SARS-CoV uses the cellular receptor angiotensin-converting enzyme 2 (ACE2) for cell entry, and infectivity assays confirmed that the novel CoV also uses human ACE2 for cell entry, suggesting that it might be capable of directly infecting humans. Furthermore, preliminary in vitro data suggest that the new virus has broad species tropism.

Severe Acute Respiratory Syndrome Coronavirus Replication Is Severely Impaired by MG132 due to Proteasome-Independent Inhibition of M-Calpain

The ubiquitin-proteasome system (UPS) is involved in the replication of a broad range of viruses. Since replication of the murine hepatitis virus (MHV) is impaired upon proteasomal inhibition, the relevance of the UPS for the replication of the severe acute respiratory syndrome coronavirus (SARS-CoV) was investigated in this study. We demonstrate that the proteasomal inhibitor MG132 strongly inhibits SARS-CoV replication by interfering with early steps of the viral life cycle. Surprisingly, other proteasomal inhibitors (e.g., lactacystin and bortezomib) only marginally affected viral replication, indicating that the effect of MG132 is independent of proteasomal impairment. Induction of autophagy by MG132 treatment was excluded from playing a role, and no changes in SARS-CoV titers were observed during infection of wild-type or autophagy-deficient ATG5(-/-) mouse embryonic fibroblasts overexpressing the human SARS-CoV receptor, angiotensin-converting enzyme 2 (ACE2). Since MG132 also inhibits the cysteine protease m-calpain, we addressed the role of calpains in the early SARS-CoV life cycle using calpain inhibitors III (MDL28170) and VI (SJA6017). In fact, m-calpain inhibition with MDL28170 resulted in an even more pronounced inhibition of SARS-CoV replication (>7 orders of magnitude) than did MG132. Additional m-calpain knockdown experiments confirmed the dependence of SARS-CoV replication on the activity of the cysteine protease m-calpain. Taken together, we provide strong experimental evidence that SARS-CoV has unique replication requirements which are independent of functional UPS or autophagy pathways compared to other coronaviruses. Additionally, this work highlights an important role for m-calpain during early steps of the SARS-CoV life cycle.

Mechanisms of Host Receptor Adaptation by Severe Acute Respiratory Syndrome Coronavirus

The severe acute respiratory syndrome coronavirus (SARS-CoV) from palm civets has twice evolved the capacity to infect humans by gaining binding affinity for human receptor angiotensin-converting enzyme 2 (ACE2). Numerous mutations have been identified in the receptor-binding domain (RBD) of different SARS-CoV strains isolated from humans or civets. Why these mutations were naturally selected or how SARS-CoV evolved to adapt to different host receptors has been poorly understood, presenting evolutionary and epidemic conundrums. In this study, we investigated the impact of these mutations on receptor recognition, an important determinant of SARS-CoV infection and pathogenesis. Using a combination of biochemical, functional, and crystallographic approaches, we elucidated the molecular and structural mechanisms of each of these naturally selected RBD mutations. These mutations either strengthen favorable interactions or reduce unfavorable interactions with two virus-binding hot spots on ACE2, and by doing so, they enhance viral interactions with either human (hACE2) or civet (cACE2) ACE2. Therefore, these mutations were viral adaptations to either hACE2 or cACE2. To corroborate the above analysis, we designed and characterized two optimized RBDs. The human-optimized RBD contains all of the hACE2-adapted residues (Phe-442, Phe-472, Asn-479, Asp-480, and Thr-487) and possesses exceptionally high affinity for hACE2 but relative low affinity for cACE2. The civet-optimized RBD contains all of the cACE2-adapted residues (Tyr-442, Pro-472, Arg-479, Gly-480, and Thr-487) and possesses exceptionally high affinity for cACE2 and also substantial affinity for hACE2. These results not only illustrate the detailed mechanisms of host receptor adaptation by SARS-CoV but also provide a molecular and structural basis for tracking future SARS-CoV evolution in animals.

Immunization with an attenuated severe acute respiratory syndrome coronavirus deleted in E protein protects against lethal respiratory disease

The severe acute respiratory syndrome coronavirus (SARS-CoV) caused substantial morbidity and mortality in 2002–2003. Deletion of the envelope (E) protein modestly diminished virus growth in tissue culture but abrogated virulence in animals. Here, we show that immunization with rSARS-CoV-ΔE or SARS-CoV-Δ[E,6-9b] (deleted in accessory proteins (6, 7a, 7b, 8a, 8b, 9b) in addition to E) nearly completely protected BALB/c mice from fatal respiratory disease caused by mouse-adapted SARS-CoV and partly protected hACE2 Tg mice from lethal disease. hACE2 Tg mice, which express the human SARS-CoV receptor, are extremely susceptible to infection. We also show that rSARS-CoV-ΔE and rSARS-CoV-Δ[E,6-9b] induced anti-virus T cell and antibody responses. Further, the E-deleted viruses were stable after 16 blind passages through tissue culture cells, with only a single mutation in the surface glycoprotein detected. The passaged virus remained avirulent in mice. These results suggest that rSARS-CoV-ΔE is an efficacious vaccine candidate that might be useful if SARS recurred.

Intraspecies diversity of SARS-like coronaviruses in Rhinolophus sinicus and its implications for the origin of SARS coronaviruses in humans

The Chinese rufous horseshoe bat (Rhinolophus sinicus) has been suggested to carry the direct ancestor of severe acute respiratory syndrome (SARS) coronavirus (SCoV), and the diversity of SARS-like CoVs (SLCoV) within this Rhinolophus species is therefore worth investigating. Here, we demonstrate the remarkable diversity of SLCoVs in R. sinicus and identify a strain with the same pattern of phylogenetic incongruence (i.e. an indication of recombination) as reported previously in another SLCoV strain. Moreover, this strain possesses a distinctive 579 nt deletion in the nsp3 region that was also found in a human SCoV from the late-phase epidemic. Phylogenetic analysis of the Orf1 region suggested that the human SCoVs are phylogenetically closer to SLCoVs in R. sinicus than to SLCoVs in other Rhinolophus species. These findings reveal a closer evolutionary linkage between SCoV in humans and SLCoVs in R. sinicus, defining the scope of surveillance to search for the direct ancestor of human SCoVs.

Angiotensin-converting enzyme 2 (ACE2) from raccoon dog can serve as an efficient receptor for the spike protein of severe acute respiratory syndrome coronavirus

Raccoon dog is one of the suspected intermediate hosts of severe acute respiratory syndrome coronavirus (SARS-CoV). In this study, the angiotensin-converting enzyme 2 (ACE2) gene of raccoon dog (rdACE2) was cloned and sequenced. The amino acid sequence of rdACE2 has identities of 99.3, 89.2, 83.9 and 80.4 % to ACE2 proteins from dog, masked palm civet (pcACE2), human (huACE2) and bat, respectively. There are six amino acid changes in rdACE2 compared with huACE2, and four changes compared with pcACE2, within the 18 residues of ACE2 known to make direct contact with the SARS-CoV S protein. A HeLa cell line stably expressing rdACE2 was established; Western blot analyses and an enzyme-activity assay indicated that the cell line expressed ACE2 at a similar level to two previously established cell lines that express ACE2 from human and masked palm civet, respectively. Human immunodeficiency virus-backboned pseudoviruses expressing spike proteins derived from human SARS-CoV or SARS-CoV-like viruses of masked palm civets and raccoon dogs were tested for their entry efficiency into these cell lines. The results showed that rdACE2 is a more efficient receptor for human SARS-CoV, but not for SARS-CoV-like viruses of masked palm civets and raccoon dogs, than huACE2 or pcACE2. This study provides useful data to elucidate the role of raccoon dog in SARS outbreaks.

Humoral and Cellular Immune Responses Induced by 3a DNA Vaccines against Severe Acute Respiratory Syndrome (SARS) or SARS-Like Coronavirus in Mice

Vaccine development for severe acute respiratory syndrome coronavirus (SARS-CoV) has mainly focused on the spike (S) protein. However, the variation of the S gene between viruses may affect the efficacy of a vaccine, particularly for cross-protection against SARS-like CoV (SL-CoV). Recently, a more conserved group-specific open reading frame (ORF), the 3a gene, was found in both SARS-CoV and SL-CoV. Here, we studied the immunogenicity of human SARS-CoV 3a and bat SL-CoV 3a DNA vaccines in mice through electroporation immunization followed by enzyme-linked immunosorbent, enzyme-linked immunospot, and flow cytometry assays. Our results showed that high levels of specific humoral responses were induced by SARS-CoV 3a and SL-CoV 3a DNA vaccines. Furthermore, a strong Th1-based cellular immune response was stimulated by both DNA vaccines. The vaccines stimulated gamma interferon production mainly by CD8(+) T cells and interleukin-2 (IL-2) mainly by CD4(+) T cells. Of interest, the frequency of IL-2-positive cells elicited by the SARS-CoV 3a DNA vaccine was significantly higher than that elicited by the SL-CoV 3a DNA vaccine. In summary, our study provides a reference for designing cross-protective DNA vaccines based on the group-specific ORFs of CoVs.

Structural Analysis of Major Species Barriers between Humans and Palm Civets for Severe Acute Respiratory Syndrome Coronavirus Infections

It is believed that a novel coronavirus, severe acute respiratory syndrome coronavirus (SARS-CoV), was passed from palm civets to humans and caused the epidemic of SARS in 2002 to 2003. The major species barriers between humans and civets for SARS-CoV infections are the specific interactions between a defined receptor-binding domain (RBD) on a viral spike protein and its host receptor, angiotensin-converting enzyme 2 (ACE2). In this study a chimeric ACE2 bearing the critical N-terminal helix from civet and the remaining peptidase domain from human was constructed, and it was shown that this construct has the same receptor activity as civet ACE2. In addition, crystal structures of the chimeric ACE2 complexed with RBDs from various human and civet SARS-CoV strains were determined. These structures, combined with a previously determined structure of human ACE2 complexed with the RBD from a human SARS-CoV strain, have revealed a structural basis for understanding the major species barriers between humans and civets for SARS-CoV infections. They show that the major species barriers are determined by interactions between four ACE2 residues (residues 31, 35, 38, and 353) and two RBD residues (residues 479 and 487), that early civet SARS-CoV isolates were prevented from infecting human cells due to imbalanced salt bridges at the hydrophobic virus/receptor interface, and that SARS-CoV has evolved to gain sustained infectivity for human cells by eliminating unfavorable free charges at the interface through stepwise mutations at positions 479 and 487. These results enhance our understanding of host adaptations and cross-species infections of SARS-CoV and other emerging animal viruses.