The 442th amino acid residue of the spike protein is critical for the adaptation to bat hosts for SARS-related coronaviruses.

Bats carry diverse severe acute respiratory syndrome-related coronaviruses (SARSr-CoVs). The suspected interspecies transmission of SARSr-CoVs from bats to humans has caused two severe CoV pandemics, the SARS pandemic in 2003 and the recent COVID-19 pandemic. The receptor utilization of SARSr-CoV plays the key role in determining the host range and the interspecies transmission ability of the virus. Both SARS-CoV and SARS-CoV-2 use angiotensin-converting enzyme 2 (ACE2) as their receptor. Previous studies showed that WIV1 strain, the first living coronavirus isolated from bat using ACE2 as its receptor, is the prototype of SARS-CoV. The receptor-binding domain (RBD) in the spike protein (S) of SARS-CoV and WIV1 is responsible for ACE2 binding and medicates the viral entry. Comparing to SARS-CoV, WIV1 has three distinct amino acid residues (442, 472, and 487) in its RBD. This study aimed at exploring whether these three residues could alter the receptor utilization of SARSr-CoVs. We replaced the three residues in SARS-CoV (BJ01 strain) S with their counterparts in WIV1 S, and then evaluated the change of their utilization of bat, civet, and human ACE2s using a lentivirus-based pseudovirus infection system. To further validate the S-ACE2 interactions, the binding affinity between the RBDs of these S proteins and the three ACE2s were verified by flow cytometry. The results showed that the single amino acid substitution Y442S in the RBD of BJ01 S enhanced its utilization of bat ACE2 and its binding affinity to bat ACE2. On the contrary, the reverse substitution in WIV1 S (S442Y) significantly attenuated the pseudovirus utilization of bat, civet and human ACE2s for cell entry, and reduced its binding affinity with the three ACE2s. These results suggest that the S442 is critical for WIV1 adapting to bats as its natural hosts. These findings will enhance our understanding of host adaptations and cross-species infections of coronaviruses, contributing to the prediction and prevention of coronavirus epidemics.

Receptor utilization of angiotensin-converting enzyme 2 (ACE2) indicates a narrower host range of SARS-CoV-2 than that of SARS-CoV.

Coronavirus (CoV) pandemics have become a huge threat to the public health worldwide in the recent decades. Typically, severe acute respiratory syndrome CoV (SARS-CoV) caused SARS pandemic in 2003 and SARS-CoV-2 caused the ongoing COVID-19 pandemic. Both viruses are most likely originated from bats. Thus, direct or indirect inter-species transmission from bats to humans is required for the viruses to cause pandemics. Receptor utilization is a key factor determining the host range of viruses which is critical to the inter-species transmission. Angiotensin-converting enzyme 2 (ACE2) is the receptor of both SARS-CoV and SARS-CoV-2, but only ACE2s of certain animals can be utilized by the viruses. Here, we employed pseudovirus cell-entry assay to evaluate the receptor-utilizing capability of ACE2s of 20 animals by the two viruses and found that SARS-CoV-2 utilized less ACE2s than SARS-CoV, indicating a narrower host range of SARS-CoV-2. Especially, SARS-CoV-2 tended not to use murine or non-mammal ACE2s. Meanwhile, pangolin-CoV, another SARS-related coronavirus highly homologous to SARS-CoV-2 in its genome, yet showed similar ACE2 utilization profile with SARS-CoV rather than SARS-CoV-2. Nevertheless, the actual susceptibility of these animals to the coronaviruses should be further verified by in vivo studies. To clarify the mechanism underlying the receptor utilization, we compared the amino acid sequences of the 20 ACE2s and found 5 amino acid residues potentially critical for ACE2 utilization, including the N-terminal 20th and 42nd amino acid residues that might determine the different receptor utilization of SARS-CoV, SARS-CoV-2 and pangolin-CoV. Our studies enhance the understanding of receptor utilization of pandemic coronaviruses, potentially contributing to the virus tracing, intermediate host screening and epidemic prevention for pathogenic coronaviruses.

Evaluation of the exposure risk of SARS-CoV-2 in different hospital environment.

The ongoing coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has imposed a significant impact on social and economic activities. As a high infectious pathogen, the existence of SARS-CoV-2 in public space is very important for its transmission. During the COVID-19 pandemic, hospitals are the main places to deal with the diseases. In this work, we evaluated the exposure risk of SARS-CoV-2 in hospital environment in order to protect healthcare workers (HCWs). Briefly, air and surface samples from 6 different sites of 3 hospitals with different protection levels were collected and tested for the SARS-CoV-2 nucleic acid by reverse transcription real-time fluorescence PCR method during the COVID-19 epidemic. We found that the positive rate of SARS-CoV-2 nucleic acid was 7.7 % in a COVID-19 respiratory investigation wards and 82.6 % in a ICUs with confirmed COVID-19 patients. These results indicated that in some wards of the hospital, such as ICUs occupied by COVID-19 patients, the nucleic acid of SARS-CoV-2 existed in the air and surface, which indicates the potential occupational exposure risk of HCWs. This study has clarified retention of SARS-CoV-2 in different sites of hospital, suggesting that it is necessary to monitor and disinfect the SARS-CoV-2 in hospital environment during COVID-19 pandemic, and will help to prevent the iatrogenic infection and nosocomial transmission of SARS-CoV-2 and to better protect the HCWs.

The ORF6, ORF8 and nucleocapsid proteins of SARS-CoV-2 inhibit type I interferon signaling pathway.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel human coronavirus causing the pandemic of severe pneumonia (Coronavirus Disease 2019, COVID-19). SARS-CoV-2 is highly pathogenic in human, having posed immeasurable public health challenges to the world. Innate immune response is critical for the host defense against viral infection and the dysregulation of the host innate immune responses probably aggravates SARS-CoV-2 infection, contributing to the high morbidity and lethality of COVID-19. It has been reported that some coronavirus proteins play an important role in modulating innate immunity of the host, but few studies have been conducted on SARS-CoV-2. In this study, we screened the viral proteins of SARS-CoV-2 and found that the viral ORF6, ORF8 and nucleocapsid proteins were potential inhibitors of type I interferon signaling pathway, a key component for antiviral response of host innate immune. All the three proteins showed strong inhibition on type I interferon (IFN-ß) and NF-κB-responsive promoter, further examination revealed that these proteins were able to inhibit the interferon-stimulated response element (ISRE) after infection with Sendai virus, while only ORF6 and ORF8 proteins were able to inhibit the ISRE after treatment with interferon beta. These findings would be helpful for the further study of the detailed signaling pathway and unveil the key molecular player that may be targeted.

Predicting the angiotensin converting enzyme 2 (ACE2) utilizing capability as the receptor of SARS-CoV-2.

SARS-CoV-2, the newly identified human coronavirus causing severe pneumonia pandemic, was probably originated from Chinese horseshoe bats. However, direct transmission of the virus from bats to humans is unlikely due to lack of direct contact, implying the existence of unknown intermediate hosts. Angiotensin converting enzyme 2 (ACE2) is the receptor of SARS-CoV-2, but only ACE2s of certain species can be utilized by SARS-CoV-2. Here, we evaluated and ranked the receptor-utilizing capability of ACE2s from various species by phylogenetic clustering and sequence alignment with the currently known ACE2s utilized by SARS-CoV-2. As a result, we predicted that SARS-CoV-2 tends to utilize ACE2s of various mammals, except murines, and some birds, such as pigeon. This prediction may help to screen the intermediate hosts of SARS-CoV-2.