Arteriviruses are a family of single-stranded, positive-sense RNA (+ssRNA) viruses that infect diverse animal hosts. Many arteriviruses are macrophage-tropic, consistent with their utilization of the macrophage-specific molecule CD163 as a receptor. However, the horse arterivirus (equine arteritis virus, EAV), which infects additional cell types beyond macrophages, does not utilize CD163 in its entry mechanism. Here, we use a genome-wide CRISPR knockout screen to identify alternative receptors that could explain this discrepancy in arterivirus receptor utilization and tropism, identifying the plasma membrane tetraspanin CD81 as a required host factor for EAV infection. Genetic knockout of CD81 or pre-incubation with soluble CD81 protected cells from infection with EAV, but had no impact on susceptibility to other arteriviruses. Bypassing the entry step of the viral life cycle by transfecting the EAV genome into CD81-knockout cells produced infectious EAV, implicating CD81 in the EAV entry process. Screening of CD81 orthologs from natural arterivirus hosts identified the brushtail possum CD81 as unsupportive of EAV entry, indicating that CD81 incompatibility can serve as a barrier to cross-species infection. Horse/possum CD81 chimeras were then used to map the structural domains of CD81 engaged by EAV, identifying alpha helix "D" on the large extracellular loop of CD81 as critical for EAV entry. This study identifies the first example of receptor switching in the Arteriviridae family and, given the broad tissue distribution of CD81 expression, suggests that the adoption of CD81 enabled an expansion of EAV tropism.IMPORTANCEArteriviruses are a family of diverse positive-sense RNA viruses that can infect a wide range of animal hosts, but many details regarding how arteriviruses gain entry into cells remain unclear. Most arteriviruses are thought to utilize the macrophage-specific molecule CD163 as a receptor; however, the horse arterivirus (equine arteritis virus, EAV) infects additional cell types beyond macrophages and does not utilize CD163. In this study, we identified the host factor CD81 as a significant player in EAV entry. Beyond the implications that this discovery holds for equine health, this study adds to the increasingly complex picture of arterivirus entry and demonstrates that these viruses are capable of adopting new host molecules as receptors, with consequences for the types of cells these viruses infect, the disease they cause, and their mode(s) of transmission.

Over the past two decades, various coronaviruses have posed a severe threat to human life and health, with the spike protein (S protein) being a critical protein for infecting host cells. Glycyrrhizic acid (GA), as a natural drug, can inhibit the infection of coronaviruses by binding to the receptor-binding domain (RBD) of the S protein. However, issues like poor water solubility and weak binding affinity with the S protein have hindered its further application. Therefore, drawing inspiration from the biological structure of centipedes, a ROS-responsive multi-branched drug conjugate (ODPAG) was constructed through a "polymer-drug linkage" strategy using dextran as the backbone and GA as the active "claw". ODPAG exhibited drug loading of 22.0 ± 0.2% (OD40kPAG) and 19.7 ± 0.1% (OD450kPAG), showing ROS responsiveness with a half-life 6.4 times that of GA (OD40kPAG) and 5.4 times longer (OD450kPAG). In in vitro antiviral experiments, ODPAG exhibited an enhanced binding affinity to the S protein, with IC50 values of 1.33 μM (OD40kPAG) and 0.89 μM (OD450kPAG) against SARS-CoV-2 pseudovirus, demonstrating exceptional antiviral efficacy. These results collectively indicate that ODPAG can block coronavirus infection by binding to the S protein, exhibiting significant potential in addressing the current challenges posed by the novel coronavirus. Additionally, the "polymer-drug conjugate" strategy employed in this process is efficient, cost-effective, and offers new insights for combating future emergent coronaviruses.

Three studies recently published in Cell reveal distinct ACE2 binding interactions across the merbecoviruses, uncovering how HKU5 can use ACE2s of many non-human hosts and identifying a novel HKU5 lineage capable of using human ACE2. These findings highlight merbecovirus receptor plasticity and caution for preparedness against potential merbecovirus threats.

Sarbecoviruses, such as SARS-CoV-2, utilize angiotensin-converting enzyme 2 (ACE2) as the entry receptor; while merbecoviruses, such as MERS-CoV, use dipeptidyl peptidase 4 (DPP4) for viral entry. Recently, several MERS-related coronaviruses, NeoCoV and PDF-2180, were reported to use ACE2, the same receptor as SARS-CoV-2, to enter cells, raising the possibility of potential recombination between SARS-CoV-2 and MERS-related coronaviruses within the co-infected ACE2-expressing cells. However, facing this potential recombination risk, the serum and antibody cross-reactivity against MERS/MERS-related coronaviruses after SARS-CoV-2 vaccination and/or infection is still elusive. Here, in this study, we showed that the serological cross-reactivity against MERS/MERS-related S proteins could be induced by SARS-CoV-2 infection but not by inactivated SARS-CoV-2 vaccination. Further investigation revealed that this serum cross-reactivity is due to monoclonals recognizing relatively conserved S2 epitopes, such as fusion peptide and stem helix, but not by antibodies against the receptor-binding domain (RBD), N-terminal domain (NTD) or subdomain-1 (SD1). Some of these anti-S2 cross-reactive mAbs showed cross-neutralizing activity, while none of them exhibited antibody-dependent enhancement (ADE) effect of viral entry in vitro. Together, these results dissected the SARS-CoV-2 infection-induced serological cross-reactivity against MERS/MERS-related coronaviruses, and highlighted the significance of conserved S2 region for the design and development of pan-β-coronaviruses vaccines.

DPP4 was considered a canonical receptor for merbecoviruses until the recent discovery of African bat-borne MERS-related coronaviruses using ACE2. The extent and diversity of ACE2 utilization among merbecoviruses and their receptor species tropism remain unknown. Here, we reveal that HKU5 enters host cells utilizing Pipistrellus abramus (P.abr) and several non-bat mammalian ACE2s through a binding mode distinct from that of any other known ACE2-using coronaviruses. We defined the molecular determinants of receptor species tropism and identified a single amino acid mutation enabling HKU5 to utilize human ACE2, providing proof of principle for machine-learning-assisted outbreak preparedness. We show that MERS-CoV and HKU5 have markedly distinct antigenicity and identified several HKU5 inhibitors, including two clinical compounds. Our findings profoundly alter our understanding of coronavirus evolution, as several merbecovirus clades independently evolved ACE2 utilization, and pave the way for developing countermeasures against viruses poised for human emergence.

Merbecoviruses comprise four viral species with remarkable genetic diversity: MERS-related coronavirus, Tylonycteris bat coronavirus HKU4, Pipistrellus bat coronavirus HKU5, and Hedgehog coronavirus 1. However, the potential human spillover risk of animal merbecoviruses remains to be investigated. Here, we reported the discovery of HKU5-CoV lineage 2 (HKU5-CoV-2) in bats that efficiently utilize human angiotensin-converting enzyme 2 (ACE2) as a functional receptor and exhibits a broad host tropism. Cryo-EM analysis of HKU5-CoV-2 receptor-binding domain (RBD) and human ACE2 complex revealed an entirely distinct binding mode compared with other ACE2-utilizing merbecoviruses with RBD footprint largely shared with ACE2-using sarbecoviruses and NL63. Structural and functional analyses indicate that HKU5-CoV-2 has a better adaptation to human ACE2 than lineage 1 HKU5-CoV. Authentic HKU5-CoV-2 infected human ACE2-expressing cell lines and human respiratory and enteric organoids. This study reveals a distinct lineage of HKU5-CoVs in bats that efficiently use human ACE2 and underscores their potential zoonotic risk.

Three studies published in this issue of Cell reveal that multiple MERS-related coronaviruses (MERSr-CoVs) utilize ACE2, rather than the canonical Merbecovirus receptor DPP4, for cell entry. These ACE2-dependent MERSr-CoVs pose a risk of zoonotic transmission to humans with high transmissibility potential like SARS-CoV-2, thus calling for global surveillance and countermeasures.

The angiotensin-converting enzyme 2 (ACE2) receptor is shared by various coronaviruses with distinct receptor-binding domain (RBD) architectures, yet our understanding of these convergent acquisition events remains elusive. Here, we report that two bat MERS-related coronaviruses (MERSr-CoVs) infecting Pipistrellus nathusii (P.nat)-MOW15-22 and PnNL2018B-use ACE2 as their receptor, with narrow ortholog specificity. Cryoelectron microscopy structures of the MOW15-22/PnNL2018B RBD-ACE2 complexes unveil an unexpected and entirely distinct binding mode, mapping >45 Å away from that of any other known ACE2-using coronaviruses. Functional profiling of ACE2 orthologs from 105 mammalian species led to the identification of host tropism determinants, including an ACE2 N432-glycosylation restricting viral recognition, and the design of a soluble P.nat ACE2 mutant with potent viral neutralizing activity. Our findings reveal convergent acquisition of ACE2 usage for merbecoviruses found in European bats, underscoring the extraordinary diversity of ACE2 recognition modes among coronaviruses and the promiscuity of this receptor.

Dipeptidyl peptidase-4 (DPP4) is a well-established receptor for several MERS-related coronaviruses (MERSr-CoVs) isolated from humans, camels, pangolins, and bats 1-6. However, the receptor usage of many genetically diverse bat MERSr-CoVs with broad geographical distributions remains poorly understood. Recent studies have identified angiotensin-converting enzyme 2 (ACE2) as an entry receptor for multiple merbecovirus clades. Here, using viral antigen and pseudovirus-based functional assays, we demonstrate that several bat merbecoviruses from the HKU25 clade previously thought to utilize DPP4 7, employ ACE2 as their functional receptor. Cryo-electron microscopy analysis revealed that HsItaly2011 and VsCoV-a7 recognize ACE2 with a binding mode sharing similarity with that of HKU5 but involving remodeled interfaces and distinct ortholog selectivity, suggesting a common evolutionary origin of ACE2 utilization for these two clades of viruses. EjCoV-3, a strain closely related to the DPP4-using MERSr-CoV BtCoV-422, exhibited relatively broad ACE2 ortholog tropism and could utilize human ACE2 albeit suboptimally. Despite differences in entry mechanisms and spike proteolytic activation compared to MERS-CoV, these viruses remain sensitive to several broadly neutralizing antibodies and entry inhibitors. These findings redefine our understanding of the evolution of receptor usage among MERSr-CoVs and highlight the versatility of ACE2 as a functional receptor for diverse coronaviruses.

Particulate matter 2.5 (PM2.5) pollution and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic are the greatest environmental health issues worldwide. Several statistics revealed the significant positive correlation between the morbidity of coronavirus disease-19 (COVID-19) and the levels of air pollution. Nevertheless, there is no direct experimental evidence to indicate the effect of PM2.5 exposure on SARS-CoV-2 infection. The objective of this study was to evaluate whether the infection of SARS-CoV-2 affected by PM2.5 through angiotensin-converting enzyme II (ACE2) expression enhances and investigate the function of ACE2 in lung injury induced by PM2.5. An animal model of PM2.5-induced lung injury was established using wild-type (WT, C57BL/6), human ACE2 transgenic (K18-hACE2 TG), and murine ACE2 gene knockout (mACE2 KO) mice. The results indicate that PM2.5 exposure facilitates SARS-CoV-2 infection through inducing ACE2 expression in vitro (10 μg/mL) and in vivo (6.25 mg/kg/day in 50 μL saline). The levels of ACE, inflammatory cytokines, and mitogen-activated protein kinase (MAPK) proteins in WT, K18-hACE TG and mACE2 KO mice were significantly increased after PM2.5 instillation. The severest PM2.5-induced lung damage was observed in mACE2 KO mice. In summary, ACE2 plays a double-edged sword role in lung injury, PM2.5 exposure contributed to SARS-CoV-2 infection through inducing ACE2 expression, but ACE2 also protected pulmonary inflammation from PM2.5 challenge.

Coronaviridae spike glycoproteins mediate viral entry and fusion to host cells through binding to host receptors (i.e., ACE2, DPP4) and are key components in determining viral host range, making them targets for antiviral research. Here, we describe the expression, purification, and characterization of recombinant spike proteins to aid in protein characterization and analysis. These protocols were used for the production of spike glycoproteins from civet, pangolin, and bat coronaviruses, as well as high-resolution cryo-electron microscopy (cryo-EM) structural analysis of bat and civet host coronavirus spike glycoproteins (Hills et al., 2024). © 2025 The Author(s). Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Expression and purification of SARS-CoV spike protein from ExpiCHO cells Basic Protocol 2: Preparation of SARS-CoV spike protein for visualization by negative-stain transmission electron microscopy and cryo-electron microscopy.

The frequency of zoonotic viral emergence within the Coronaviridae family highlights the critical need to understand the structural features of spike proteins that govern viral entry and host adaptation. Investigating the structural conservation and variation in key regions of the spike protein-those involved in host range, binding affinity, viral entry, and immune evasion-is essential for predicting the evolutionary pathways of coronaviruses, assessing the risk of future host-jumping events, and discovering pan-neutralising antibodies. Here we summarise our current structural understanding of the spike proteins similar to SARS-CoV-2 from the Coronaviridae family and compare key functional similarities and differences. Our aim is to demonstrate the significant structural and sequence conservation between spike proteins from a range of host species and to outline the importance of animal coronavirus surveillance and structural investigation in our endeavour for pandemic preparedness against emerging viruses.

Coronaviruses (CoV) emerge suddenly from animal reservoirs to cause novel diseases in new hosts. Discovered in 2012, the Middle East respiratory syndrome coronavirus (MERS-CoV) is endemic in camels in the Middle East and is continually causing local outbreaks and epidemics. While all three newly emerging human CoVs from the past 20 years (SARS-CoV, SARS-CoV-2, and MERS-CoV) cause respiratory disease, each CoV has unique host interactions that drive differential pathogeneses. To better understand the virus and host interactions driving lethal MERS-CoV infection, we performed a longitudinal multi-omics analysis of sublethal and lethal MERS-CoV infection in mice. Significant differences were observed in body weight loss, virus titers, and acute lung injury among lethal and sub-lethal virus doses. Virus-induced apoptosis of type I and II alveolar epithelial cells suggests that loss or dysregulation of these key cell populations was a major driver of severe disease. Omics analysis suggested differential pathogenesis was multi-factorial with clear differences among innate and adaptive immune pathways as well as those that regulate lung epithelial homeostasis. Infection of mice lacking functional T and B cells showed that adaptive immunity was important in controlling viral replication but also increased pathogenesis. In summary, we provide a high-resolution host response atlas for MERS-CoV infection and disease severity. Multi-omics studies of viral pathogenesis offer a unique opportunity to not only better understand the molecular mechanisms of disease but also to identify genes and pathways that can be exploited for therapeutic intervention all of which is important for our future pandemic preparedness.IMPORTANCEEmerging coronaviruses like SARS-CoV, SARS-CoV-2, and MERS-CoV cause a range of disease outcomes in humans from an asymptomatic, moderate, and severe respiratory disease that can progress to death but the factors causing these disparate outcomes remain unclear. Understanding host responses to mild and life-threatening infections provides insight into virus-host networks within and across organ systems that contribute to disease outcomes. We used multi-omics approaches to comprehensively define the host response to moderate and severe MERS-CoV infection. Severe respiratory disease was associated with dysregulation of the immune response. Key lung epithelial cell populations that are essential for lung function get infected and die. Mice lacking key immune cell populations experienced greater virus replication but decreased disease severity implicating the immune system in both protective and pathogenic roles in response to MERS-CoV. These data could be utilized to design new therapeutic strategies targeting specific pathways that contribute to severe disease.

Dipeptidyl peptidase-4 (DPP4) is a well-established receptor for several MERS-related coronaviruses (MERSr-CoVs) isolated from humans, camels, pangolins, and bats (1-6). However, the receptor usage of many genetically diverse bat MERSr-CoVs with broad geographical distributions remains poorly understood. Recent studies have identified angiotensin-converting enzyme 2 (ACE2) as an entry receptor for multiple merbecovirus clades. Here, using viral antigen and pseudovirus-based functional assays, we demonstrate that several bat merbecoviruses from the HKU25 clade previously thought to utilize DPP4 (7), employ ACE2 as their functional receptor. Cryo-electron microscopy analysis revealed that HsItaly2011 and VsCoV-a7 recognize ACE2 with a binding mode sharing similarity with that of HKU5 but involving remodeled interfaces and distinct ortholog selectivity, suggesting a common evolutionary origin of ACE2 utilization for these two clades of viruses. EjCoV-3, a strain closely related to the DPP4-using MERSr-CoV BtCoV-422, exhibited relatively broad ACE2 ortholog tropism and could utilize human ACE2 albeit suboptimally. Despite differences in entry mechanisms and spike proteolytic activation compared to MERS-CoV, these viruses remain sensitive to several broadly neutralizing antibodies and entry inhibitors. These findings redefine our understanding of the evolution of receptor usage among MERSr-CoVs and highlight the versatility of ACE2 as a functional receptor for diverse coronaviruses.

Recent studies unexpectedly revealed that several merbecoviruses convergently evolved ACE2 receptor usage with distinct binding modes across three continents, challenging the dogma that DPP4 is their primary receptor. Here, we demonstrate that HKU25 clade MERS-related coronaviruses broadly distributed across Eurasia utilize ACE2 as host receptor through a binding mode shared with HKU5, challenging prior findings. These findings reveal a prevalence of ACE2 usage in diverse MERS-related coronaviruses in bats and show that EjCoV-3 is preadapted to use human ACE2, suggesting a potential for spillover. Our data provide a blueprint of host receptor barrier determinants which will facilitate global surveillance and development of countermeasures against these poorly characterized merbecoviruses.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters host cells via the angiotensin-converting enzyme 2 (ACE2) receptor. Mounting evidence has indicated the presence of hepatic SARS-CoV-2 infection and liver injury in patients with coronavirus disease 2019 (COVID-19). Understanding the mechanisms of hepatic SARS-CoV-2 infection is crucial for addressing COVID-19-related liver pathology and developing targeted therapies. This editorial discusses the significance of ACE2 in hepatic SARS-CoV-2 infection, drawing on the research by Jacobs et al. Their findings indicate that hepatic ACE2 expression, frequency of hepatic SARS-CoV-2 infection, and severity of liver injury are elevated in patients with pre-existing chronic liver diseases. These data suggest that hepatic ACE2 could be a promising therapeutic target for COVID-19.

This study aimed to elucidate the complexity of the humoral immune response in COVID-19 patients with varying disease trajectories using a SARS-CoV-2 whole proteome peptide microarray chip. The microarray, containing 5347 peptides spanning the entire SARS-CoV-2 proteome and key variants of concern, was used to analyze IgG responses in 10 severe-to-recovered, 9 nonsevere-to-severe cases, and 10 control case (5 pre-pandemic and 5 SARS-CoV-2-negative) plasma samples. We identified 1151 IgG-reactive peptides corresponding to 647 epitopes, with 207 peptides being cross-reactive across 124 epitopes. Nonstructural protein 3 (nsp3) exhibited the highest number of total and unique epitopes, followed by the spike protein. nsp12 had the most number of cross-reactive epitopes. Peptides from the spike protein and nsps 2, 3, 5, and 13 were notably associated with recovery. Additionally, specific mutations in SARS-CoV-2 variants were found to alter peptide immunoreactivity, with some mutations (e.g., G142D, L452R, and N501Y) enhancing and others (e.g., R190S and E484 K) reducing immune recognition. These findings have critical implications for the development of diagnostics, vaccines, and therapeutics. Understanding the distribution of epitopes and the impact of viral mutations on antigenicity provides insights into immune evasion mechanisms, informing strategies for controlling COVID-19 and future coronavirus outbreaks.

We identified seven distinct coronaviruses (CoVs) in bats from Brazil, classified into 229E-related (Alpha-CoV), Nobecovirus, Sarbecovirus, and Merbecovirus (Beta-CoV), including one closely related to MERS-like CoV with 82.8% genome coverage. To accomplish this, we screened 423 oral and rectal swabs from 16 different bat species using molecular assays, RNA sequencing, and evolutionary analysis. Notably, gaps in the spike-encoding gene led us to design new primers and perform Sanger sequencing, which revealed high similarities to MERS-related (MERSr) CoV strains found in humans and camels. Additionally, we identified key residues in the receptor-binding domain (RBD) of the spike protein, suggesting potential interactions with DPP4, the receptor for MERSr-CoV. Our analyses also revealed evidence of recombination involving our laboratory-produced sequences. These findings highlight the extensive genetic diversity of CoVs, the presence of novel viral lineages, and the occurrence of recombination events among bat CoVs circulating in Brazil, underscoring the critical role bats play as reservoirs for emerging viruses and emphasizing the necessity of ongoing surveillance to monitor the public health risks associated with CoV spillover events.

Antigen recognition by human leukocyte antigen (HLA) restriction is critical for an adequate antiviral response in both natural infection and vaccination. However, the overwhelming polymorphism of HLA, with nearly 40,000 alleles identified, is an important limitation for the global analysis of cellular immune responses and vaccine efficacy. In this narrative review, we included several immunoinformatics studies performed in our laboratory to circumvent this limitation. These analyses focused on studying the cellular immune responses restricted by the most common HLA alleles, and their role in vaccine efficacy. Computational studies validated experimentally, such as our laboratory has carried out, represent a useful, rapid, and cost-effective strategy to combat future pandemics.

Porcine delta-coronavirus (PDCoV) spillovers were recently detected in febrile children, underscoring the recurrent zoonoses of divergent CoVs. To date, no vaccines or specific therapeutics are approved for use in humans against PDCoV. To prepare for possible future PDCoV epidemics, we isolated PDCoV spike (S)-directed monoclonal antibodies (mAbs) from humanized mice and found that two, designated PD33 and PD41, broadly neutralized a panel of PDCoV variants. Cryoelectron microscopy (cryo-EM) structures of PD33 and PD41 in complex with the S receptor-binding domain (RBD) and ectodomain trimer revealed the epitopes recognized by these mAbs, rationalizing their broad inhibitory activity. We show that both mAbs competitively interfere with host aminopeptidase N binding to neutralize PDCoV and used deep-mutational scanning epitope mapping to associate RBD antigenic sites with mAb-mediated neutralization potency. Our results indicate a PD33-PD41 mAb cocktail may heighten the barrier to escape. PD33 and PD41 are candidates for clinical advancement against future PDCoV outbreaks.

Human coronaviruses such as SARS-CoV, MERS-CoV, and SARS-CoV-2 have recurrently emerged as significant pathogens, causing severe respiratory illnesses and presenting challenges to monoclonal antibody therapeutics due to their rapid evolution, particularly the diverse variants of SARS-CoV-2. In this study, we utilized "Knob-into-Hole" and "IgG-scFv" technologies to engineer bispecific antibodies (bsAbs) that target both the viral receptor and spike protein, enhancing their neutralization breadth and potency. Our bsAbs, combining anti-SARS-CoV-2 or anti-MERS-CoV antibodies with an anti-ACE2 antibody, demonstrated effective neutralization across a range of SARS-CoV-2 variants, SARS-CoV and MERS-CoV in both pseudovirus and authentic virus assays. Notably, the "IgG-scFv" bsAbs format exhibited superior binding and neutralization capabilities compared to the "Knob-into-Hole" configurations. The most effective of these, "IgG-scFv" H11B11_m336, displayed exceptional neutralization potency against a panel of 24 pseudotyped Beta-Coronaviruses, with IC50 values ranging from 0.001-0.183 μg/mL. Overall, our findings underscore the potential of bsAbs as an effective strategy to meet the immediate challenges posed by existing and emerging pathogens, thereby enhancing global pandemic preparedness.

Coronaviruses (CoVs) pose a major risk to global public health due to their ability to infect diverse animal species and potential for emergence in humans. The CoV spike protein mediates viral entry into the cell and plays a crucial role in determining the binding affinity to host cell receptors. With particular emphasis on α- and β-coronaviruses that infect humans and domestic animals, current research on CoV receptor use suggests that the exploitation of the angiotensin-converting enzyme 2 (ACE2) receptor poses a significant threat for viral emergence with pandemic potential. This review summarizes the approaches used to study binding interactions between CoV spike proteins and the human ACE2 (hACE2) receptor. Solid-phase enzyme immunoassays and cell binding assays allow qualitative assessment of binding but lack quantitative evaluation of affinity. Surface plasmon resonance, Bio-layer interferometry, and Microscale Thermophoresis on the other hand, provide accurate affinity measurement through equilibrium dissociation constants (KD). In silico modeling predicts affinity through binding structure modeling, protein-protein docking simulations, and binding energy calculations but reveals inconsistent results due to the lack of a standardized approach. Machine learning and deep learning models utilize simulated and experimental protein-protein interaction data to elucidate the critical residues associated with CoV binding affinity to hACE2. Further optimization and standardization of existing approaches for studying binding affinity could aid pandemic preparedness. Specifically, prioritizing surveillance of CoVs that can bind to human receptors stands to mitigate the risk of zoonotic spillover.

The pivotal role of the cell entry receptor ACE2 for SARS-CoV-2 infection is well-established. When ACE2 is shed from cell surface into plasma as soluble ACE2 (sACE2), it can effectively neutralize SARS-CoV-2. This longitudinal prospective cohort study analyzed sACE2 activity in 1192 participants, aged 4 months to 81 years, 3 and 12 months after SARS-CoV-2 household exposure. Following SARS-CoV-2 exposure, participants exhibited significantly elevated sACE2 activity, irrespective of confirmed infection, with the highest levels observed in exposed children. Longitudinal analysis revealed a decline in sACE2 levels over time, reaching levels comparable to age- and sex-matched pre-pandemic controls. An increase in sACE2 activity was also confirmed in vitro in Calu-3 (human lung) cells within hours of SARS-CoV-2 exposure, providing a direct link between SARS-CoV-2 exposure and elevated sACE2. This study, therefore, challenges the dichotomy of categorizing SARS-CoV-2 exposed participants as infected or not infected solely on currently established diagnostic assays. It demonstrates lasting host responses independent of B- and T-cell memory and may help to keep SARS-CoV-2 infections in balance and contribute to successful virus clearance in children and adults lacking humoral and cellular immune responses following SARS-CoV-2 exposure. Trial Registration: German Registry for Clinical Studies; Identifier: D 00021521.

The discovery of alphacoronaviruses and betacoronaviruses in plateau pikas (Ochotona curzoniae) expanded the host range of mammalian coronavirus (CoV) to a new order - Lagomorpha. However, the diversity and evolutionary relationships of CoVs in these plateau-region-specific animal population remains uncertain. We conducted a five-year longitudinal surveillance of CoVs harboured by pikas around Qinghai Lake, China. CoVs were identified in 33 of 236 plateau pikas and 2 of 6 Gansu pikas (Ochotona cansus), with a total positivity rate of 14.5%, and exhibiting a wide spatiotemporal distribution across seven sampling sites and six time points. Through meta-transcriptomic sequencing and RT-PCR, we recovered 16 near-complete viral genome sequences. Phylogenetic analyses classified the viruses as variants of either pika alphacoronaviruses or betacoronaviruses endemic to plateau pikas from the Qinghai-Tibet Plateau region. Of particular note, the pika-associated betacoronaviruses may represent a novel subgenus within the genus Betacoronavirus. Tissue tropism, evaluated using quantitative real-time PCR, revealed the presence of CoV in the rectal and/or lung tissues, with the highest viral loads at 103.55 or 102.80 RNA copies/μL. Surface plasmon resonance (SPR) assays indicated that the newly identified betacoronavirus did not bind to human or pika Angiotensin-converting enzyme 2 (ACE2) or Dipeptidyl peptidase 4 (DPP4). The findings highlight the ongoing circulation and broadening host spectrum of CoVs among pikas, emphasizing the necessity for further investigation to evaluate their potential public health risks.

In the 21st century, three betacoronaviruses (SARS-CoV, MERS-CoV and SARS-CoV-2) have emerged in humans worldwide as a result of animal spillover, causing severe respiratory infections and resulting in more than seven million deaths. In 2013, a novel Betacoronavirus closely related to MERS-CoV (Betacoronavirus cameli) was discovered in European hedgehogs (Erinaceus europaeus), raising questions on the possibility of hedgehog-to-human transmission. Hence, the present study aimed to investigate and characterize the presence and genetic diversity of coronaviruses in hedgehogs from Portugal, as well as their potential for cross-species transmission. To achieve this, fecal samples from 110 hedgehogs at two recovery centers and one environmental non-governmental organization were tested for coronaviruses using a broad-spectrum nested RT-PCR assay targeting the RdRp gene. Of these samples, 24.5 % tested positive, most belonging to the Betacoronavirus genus. However, the present study also reports, for the first time, Alphacoronaviruses in hedgehogs, showing 100 % identity with a Bat coronavirus (a variant of Alphacoronavirus miniopteri). The genome sequencing of one betacoronavirus-positive sample yielded 65 % of a full-length genome, with the closest homology (93.5 %) to Betacoronavirus erinacei from the United Kingdom. Computational protein-protein docking studies predicted the binding affinity between the spike protein of hedgehog coronavirus and cell receptors of mammal species that interact with hedgehogs. The results obtained raise the question of whether hedgehog CoV uses the same receptor as MERS-CoV or a different receptor to enter host cells. Thus, this study enhances our understanding of the epidemiology of coronaviruses, emphasizing the need for further investigation into cross-species transmission risks.

Middle-East respiratory syndrome coronavirus (MERS-CoV) is a zoonotic pathogen with 36% case-fatality rate in humans. No vaccines or specific therapeutics are currently approved to use in humans or the camel host reservoir. Here, we computationally designed monomeric and homo-oligomeric miniproteins binding with high affinity to the MERS-CoV spike (S) glycoprotein, the main target of neutralizing antibodies and vaccine development. We show that these miniproteins broadly neutralize a panel of MERS-CoV S variants, spanning the known antigenic diversity of this pathogen, by targeting a conserved site in the receptor-binding domain (RBD). The miniproteins directly compete with binding of the DPP4 receptor to MERS-CoV S, thereby blocking viral attachment to the host entry receptor and subsequent membrane fusion. Intranasal administration of a lead miniprotein provides prophylactic protection against stringent MERS-CoV challenge in mice motivating future clinical development as a next-generation countermeasure against this virus with pandemic potential.

Although coronaviruses use diverse receptors, the characterization of coronaviruses with unknown receptors has been impeded by a lack of infection models1,2. Here we introduce a strategy to engineer functional customized viral receptors (CVRs). The modular design relies on building artificial receptor scaffolds comprising various modules and generating specific virus-binding domains. We identify key factors for CVRs to functionally mimic native receptors by facilitating spike proteolytic cleavage, membrane fusion, pseudovirus entry and propagation for various coronaviruses. We delineate functional SARS-CoV-2 spike receptor-binding sites for CVR design and reveal the mechanism of cell entry promoted by the N-terminal domain-targeting S2L20-CVR. We generated CVR-expressing cells for 12 representative coronaviruses from 6 subgenera, most of which lack known receptors, and show that a pan-sarbecovirus CVR supports propagation of a propagation-competent HKU3 pseudovirus and of authentic RsHuB2019A3. Using an HKU5-specific CVR, we successfully rescued wild-type and ZsGreen-HiBiT-incorporated HKU5-1 (LMH03f) and isolated a HKU5 strain from bat samples. Our study demonstrates the potential of the CVR strategy for establishing native receptor-independent infection models, providing a tool for studying viruses that lack known susceptible target cells.

The COVID-19 pandemic, caused by SARS-CoV-2, demonstrated that zoonotic transmission of animal sarbecoviruses threatens human health but the determinants of transmission are incompletely understood. Here, we show that most spike (S) proteins of horseshoe bat and Malayan pangolin sarbecoviruses employ ACE2 for entry, with human and raccoon dog ACE2 exhibiting broad receptor activity. The insertion of a multibasic cleavage site into the S proteins increased entry into human lung cells driven by most S proteins tested, suggesting that acquisition of a multibasic cleavage site might increase infectivity of diverse animal sarbecoviruses for the human respiratory tract. In contrast, two bat sarbecovirus S proteins drove cell entry in an ACE2-independent, trypsin-dependent fashion and several ACE2-dependent S proteins could switch to the ACE2-independent entry pathway when exposed to trypsin. Several TMPRSS2-related cellular proteases but not the insertion of a multibasic cleavage site into the S protein allowed for ACE2-independent entry in the absence of trypsin and may support viral spread in the respiratory tract. Finally, the pan-sarbecovirus antibody S2H97 enhanced cell entry driven by two S proteins and this effect was reversed by trypsin while trypsin protected entry driven by a third S protein from neutralization by S2H97. Similarly, plasma from quadruple vaccinated individuals neutralized entry driven by all S proteins studied, and availability of the ACE2-independent, trypsin-dependent pathway reduced neutralization sensitivity. In sum, our study reports a pathway for entry into human cells that is ACE2-independent, can be supported by TMPRSS2-related proteases and may be associated with antibody evasion.

Middle East respiratory syndrome coronavirus (MERS-CoV) and the pangolin MERS-like coronavirus MjHKU4r-CoV-1 employ dipeptidyl peptidase 4 (DPP4) as an entry receptor. MjHKU4r-CoV-1 could infect transgenic mice expressing human DPP4. To understand the mechanism of MjHKU4r-CoV-1 entry into cells, we determined the crystal structures of the receptor binding domain (RBD) of MjHKU4r-CoV-1 spike protein bound to human DPP4 (hDPP4) and Malayan pangolin DPP4 (MjDPP4), respectively. The overall hDPP4-binding mode of MjHKU4r-CoV-1 RBD is similar to that of MERS-CoV RBD. MjHKU4r-CoV-1 RBD shows higher binding affinity to hDPP4 compared to the bat MERS-like coronavirus Ty-BatCoV-HKU4. Via swapping residues between MjHKU4r-CoV-1 RBD and Ty-BatCoV-HKU4 RBD, we identified critical determinants on MjHKU4r-CoV-1 that are responsible for virus usage of hDPP4. Our study suggests that MjHKU4r-CoV-1 is more adapted to the human receptor compared to the bat HKU4 coronavirus and highlights the potential of virus emergence into the human population.

Our comprehensive understanding of the multi-species ACE2 adaptiveness of sarbecoviruses remains elusive, particularly for those with various receptor binding motif (RBM) insertions/deletions (indels). Here, we analyzed RBM sequences from 268 sarbecoviruses categorized into four RBM indel types. We examined the ability of 20 representative sarbecovirus Spike glycoproteins (S) and derivatives in utilizing ACE2 from various bats and several other mammalian species. We reveal that sarbecoviruses with long RBMs (type-I) can achieve broad ACE2 tropism, whereas viruses with single deletions in Region 1 (type-II) or Region 2 (type-III) exhibit narrower ACE2 tropism. Sarbecoviruses with double region deletions (type-IV) completely lost ACE2 usage, which is restricted by clade-specific residues within and outside RBM. Lastly, we propose the evolution of sarbecovirus RBM indels and illustrate how loop lengths, disulfide, and residue determinants shape multi-species ACE2 adaptiveness. This study provides profound insights into the mechanisms governing ACE2 usage and spillover risks of sarbecoviruses.

The conventional detection model of passive adaptation to pathogen mutations, i.e., developing assays using corresponding antibodies or nucleic acid probes, is difficult to address frequent outbreaks of emerging infectious diseases. In particular, adaptive mutations observed in coronaviruses, which increase the affinity of the spike protein with the human cellular receptor hACE2, play pivotal roles in the transmission and immune evasion of coronaviruses. Herein, we developed a multifunctional optical fiber evanescent wave biosensor for the universal assay of coronavirus and affinity analysis of the spike protein interacting with hACE2, namely, My-SPACE. By competitively binding with Cy5.5-hACE2 between coronavirus spike proteins in mobile buffer and that modified on optical fibers from the SARS-CoV-2 wild type, My-SPACE could automatically detect SARS-CoV-2 and its variants within 10 min. My-SPACE demonstrated greater sensitivity and faster results than ELISA for SARS-CoV-2 variants, achieving 100% specificity and 94.10% sensitivity in detecting the Omicron variant in 18 clinical samples. Moreover, the interaction between hACE2 and the coronavirus spike protein was accurately characterized across SARS-CoV-2 mutants, SARS-CoV and hCoV-NL63. The accuracy of the affinity determined by My-SPACE was verified by SPR. This approach enables preliminary assessment of the transmissibility and hazards of emerging coronaviruses. The sensor fibers of My-SPACE can be reused more than 40 times, and the device is compact and easy to use; moreover, it is available as a rapid and cost-effective on-site detection tool adapted to coronavirus variability and as an effective assessment platform for early warning of coronavirus transmission risk.