The binding and structural basis of fox ACE2 to RBDs from different sarbecoviruses.

Foxes are susceptible to SARS-CoV-2 in laboratory settings, and there have also been reports of natural infections of both SARS-CoV and SARS-CoV-2 in foxes. In this study, we assessed the binding capacities of fox ACE2 to important sarbecoviruses, including SARS-CoV, SARS-CoV-2, and animal-origin SARS-CoV-2 related viruses. Our findings demonstrated that fox ACE2 exhibits broad binding capabilities to receptor-binding domains (RBDs) of sarbecoviruses. We further determined the cryo-EM structures of fox ACE2 complexed with RBDs of SARS-CoV, SARS-CoV-2 prototype (PT), and Omicron BF.7. Through structural analysis, we identified that the K417 mutation can weaken the ability of SARS-CoV-2 sub-variants to bind to fox ACE2, thereby reducing the susceptibility of foxes to SARS-CoV-2 sub-variants. In addition, the Y498 residue in the SARS-CoV RBD plays a crucial role in forming a vital cation-π interaction with K353 in the fox ACE2 receptor. This interaction is the primary determinant for the higher affinity of the SARS-CoV RBD compared to that of the SARS-CoV-2 PT RBD. These results indicate that foxes serve as potential hosts for numerous sarbecoviruses, highlighting the critical importance of surveillance efforts.

Deciphering a reliable synergistic bispecific strategy of rescuing antibodies for SARS-CoV-2 escape variants, including BA.2.86, EG.5.1, and JN.1.

The game between therapeutic monoclonal antibodies (mAbs) and continuously emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants has favored the virus, as most therapeutic mAbs have been evaded. Addressing this challenge, we systematically explored a reproducible bispecific antibody (bsAb)-dependent synergistic effect in this study. It could effectively restore the neutralizing activity of the bsAb when any of its single mAbs is escaped by variants. This synergy is primarily attributed to the binding angle of receptor-binding domain (RBD)-5, facilitating inter-spike cross-linking and promoting cryptic epitope exposure that classical antibody cocktails cannot achieve. Furthermore, RBD-5 with RBD-2, RBD-6, and RBD-7, alongside RBD-8, also exhibit significantly enhanced effects. This study not only shifts the paradigm in understanding antibody interactions but paves the way for developing more effective therapeutic antibodies against rapidly mutating SARS-CoV-2, with Dia-19 already showing promise against emerging variants like BA.2.86, EG.5.1, and JN.1.

Neutralization of EG.5, EG.5.1, BA.2.86, and JN.1 by antisera from dimeric receptor-binding domain subunit vaccines and 41 human monoclonal antibodies.

BACKGROUND: The recently circulating Omicron variants BA.2.86 and JN.1 were identified with more than 30 amino acid changes on the spike protein compared to BA.2 or XBB.1.5. This study aimed to comprehensively assess the immune escape potential of BA.2.86, JN.1, EG.5, and EG.5.1. METHODS: We collected human and murine sera to evaluate serological neutralization activities. The participants received three doses of coronavirus disease 2019 (COVID-19) vaccines or a booster dose of the ZF2022-A vaccine (Delta-BA.5 receptor-binding domain [RBD]-heterodimer immunogen) or experienced a breakthrough infection (BTI). The ZF2202-A vaccine is under clinical trial study (ClinicalTrials.gov: NCT05850507). BALB/c mice were vaccinated with a panel of severe acute respiratory syndrome coronavirus 2 RBD-dimer proteins. The antibody evasion properties of these variants were analyzed with 41 representative human monoclonal antibodies targeting the eight RBD epitopes. FINDINGS: We found that BA.2.86 had less neutralization evasion than EG.5 and EG.5.1 in humans. The ZF2202-A booster induced significantly higher neutralizing titers than BTI. Furthermore, BA.2.86 and JN.1 exhibited stronger antibody evasion than EG.5 and EG.5.1 on RBD-4 and RBD-5 epitopes. Compared to BA.2.86, JN.1 further lost the ability to bind to several RBD-1 monoclonal antibodies and displayed further immune escape. CONCLUSIONS: Our data showed that the currently dominating sub-variant, JN.1, showed increased immune evasion compared to BA.2.86 and EG.5.1, which is highly concerning. This study provides a timely risk assessment of the interested sub-variants and the basis for updating COVID-19 vaccines. FUNDING: This work was funded by the National Key R&D Program of China, the National Natural Science Foundation of China, the Beijing Life Science Academy, the Bill & Melinda Gates Foundation, and the Postdoctoral Fellowship Program of China Postdoctoral Science Foundation (CPSF).

Molecular basis of hippopotamus ACE2 binding to SARS-CoV-2.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has a wide range of hosts, including hippopotami, which are semi-aquatic mammals and phylogenetically closely related to Cetacea. In this study, we characterized the binding properties of hippopotamus angiotensin-converting enzyme 2 (hiACE2) to the spike (S) protein receptor binding domains (RBDs) of the SARS-CoV-2 prototype (PT) and variants of concern (VOCs). Furthermore, the cryo-electron microscopy (cryo-EM) structure of the SARS-CoV-2 PT S protein complexed with hiACE2 was resolved. Structural and mutational analyses revealed that L30 and F83, which are specific to hiACE2, played a crucial role in the hiACE2/SARS-CoV-2 RBD interaction. In addition, comparative and structural analysis of ACE2 orthologs suggested that the cetaceans may have the potential to be infected by SARS-CoV-2. These results provide crucial molecular insights into the susceptibility of hippopotami to SARS-CoV-2 and suggest the potential risk of SARS-CoV-2 VOCs spillover and the necessity for surveillance. IMPORTANCE: The hippopotami are the first semi-aquatic artiodactyl mammals wherein SARS-CoV-2 infection has been reported. Exploration of the invasion mechanism of SARS-CoV-2 will provide important information for the surveillance of SARS-CoV-2 in hippopotami, as well as other semi-aquatic mammals and cetaceans. Here, we found that hippopotamus ACE2 (hiACE2) could efficiently bind to the RBDs of the SARS-CoV-2 prototype (PT) and variants of concern (VOCs) and facilitate the transduction of SARS-CoV-2 PT and VOCs pseudoviruses into hiACE2-expressing cells. The cryo-EM structure of the SARS-CoV-2 PT S protein complexed with hiACE2 elucidated a few critical residues in the RBD/hiACE2 interface, especially L30 and F83 of hiACE2 which are unique to hiACE2 and contributed to the decreased binding affinity to PT RBD compared to human ACE2. Our work provides insight into cross-species transmission and highlights the necessity for monitoring host jumps and spillover events on SARS-CoV-2 in semi-aquatic/aquatic mammals.

Key mechanistic features of the trade-off between antibody escape and host cell binding in the SARS-CoV-2 Omicron variant spike proteins.

Since SARS-CoV-2 Omicron variant emerged, it is constantly evolving into multiple sub-variants, including BF.7, BQ.1, BQ.1.1, XBB, XBB.1.5 and the recently emerged BA.2.86 and JN.1. Receptor binding and immune evasion are recognized as two major drivers for evolution of the receptor binding domain (RBD) of the SARS-CoV-2 spike (S) protein. However, the underlying mechanism of interplay between two factors remains incompletely understood. Herein, we determined the structures of human ACE2 complexed with BF.7, BQ.1, BQ.1.1, XBB and XBB.1.5 RBDs. Based on the ACE2/RBD structures of these sub-variants and a comparison with the known complex structures, we found that R346T substitution in the RBD enhanced ACE2 binding upon an interaction with the residue R493, but not Q493, via a mechanism involving long-range conformation changes. Furthermore, we found that R493Q and F486V exert a balanced impact, through which immune evasion capability was somewhat compromised to achieve an optimal receptor binding. We propose a "two-steps-forward and one-step-backward" model to describe such a compromise between receptor binding affinity and immune evasion during RBD evolution of Omicron sub-variants.

Near-gapless genome and transcriptome analyses provide insights into fruiting body development in Lentinula edodes.

Fruiting body development in macrofungi is an intensive research subject. In this study, high-quality genomes were assembled for two sexually compatible monokaryons from a heterokaryotic Lentinula edodes strain WX1, and variations in L. edodes genomes were analyzed. Specifically, differential gene expression and allele-specific expression (ASE) were analyzed using the two monokaryotic genomes and transcriptome data from four different stages of fruiting body development in WX1. Results revealed that after aeration, mycelia sensed cell wall stress, pheromones, and a decrease in CO2 concentration, leading to up-regulated expression in genes related to cell adhesion, cell wall remodeling, proteolysis, and lipid metabolism, which may promote primordium differentiation. Aquaporin genes and those related to proteolysis, mitosis, lipid, and carbohydrate metabolism may play important roles in primordium development, while genes related to tissue differentiation and sexual reproduction were active in fruiting body. Several essential genes for fruiting body development were allele-specifically expressed and the two nuclear types could synergistically regulate fruiting body development by dominantly expressing genes with different functions. ASE was probably induced by long terminal repeat-retrotransposons. Findings here contribute to the further understanding of the mechanism of fruiting body development in macrofungi.

Structural basis and analysis of hamster ACE2 binding to different SARS-CoV-2 spike RBDs.

Pet golden hamsters were first identified being infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) delta variant of concern (VOC) and transmitted the virus back to humans in Hong Kong in January 2022. Here, we studied the binding of two hamster (golden hamster and Chinese hamster) angiotensin-converting enzyme 2 (ACE2) proteins to the spike protein receptor-binding domains (RBDs) of SARS-CoV-2 prototype and eight variants, including alpha, beta, gamma, delta, and four omicron sub-variants (BA.1, BA.2, BA.3, and BA.4/BA.5). We found that the two hamster ACE2s present slightly lower affinity for the RBDs of all nine SARS-CoV-2 viruses tested than human ACE2 (hACE2). Furthermore, the similar infectivity to host cells expressing hamster ACE2s and hACE2 was confirmed with the nine pseudotyped SARS-CoV-2 viruses. Additionally, we determined two cryo-electron microscopy (EM) complex structures of golden hamster ACE2 (ghACE2)/delta RBD and ghACE2/omicron BA.3 RBD. The residues Q34 and N82, which exist in many rodent ACE2s, are responsible for the lower binding affinity of ghACE2 compared to hACE2. These findings suggest that all SARS-CoV-2 VOCs may infect hamsters, highlighting the necessity of further surveillance of SARS-CoV-2 in these animals.IMPORTANCESARS-CoV-2 can infect many domestic animals, including hamsters. There is an urgent need to understand the binding mechanism of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants to hamster receptors. Herein, we showed that two hamster angiotensin-converting enzyme 2s (ACE2s) (golden hamster ACE2 and Chinese hamster ACE2) can bind to the spike protein receptor-binding domains (RBDs) of SARS-CoV-2 prototype and eight variants and that pseudotyped SARS-CoV-2 viruses can infect hamster ACE2-expressing cells. The binding pattern of golden hamster ACE2 to SARS-CoV-2 RBDs is similar to that of Chinese hamster ACE2. The two hamster ACE2s present slightly lower affinity for the RBDs of all nine SARS-CoV-2 viruses tested than human ACE2. We solved the cryo-electron microscopy (EM) structures of golden hamster ACE2 in complex with delta RBD and omicron BA.3 RBD and found that residues Q34 and N82 are responsible for the lower binding affinity of ghACE2 compared to hACE2. Our work provides valuable information for understanding the cross-species transmission mechanism of SARS-CoV-2.

Structural basis of increased binding affinities of spikes from SARS-CoV-2 Omicron variants to rabbit and hare ACE2s reveals the expanding host tendency.

The potential host range of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been expanding alongside its evolution during the pandemic, with rabbits and hares being considered important potential hosts, supported by a report of rabbit sero-prevalence in nature. We measured the binding affinities of rabbit and hare angiotensin-converting enzyme 2 (ACE2) with receptor-binding domains (RBDs) from SARS-CoV, SARS-CoV-2, and its variants and found that rabbit and hare ACE2s had broad variant tropism, with significantly enhanced affinities to Omicron BA.4/5 and its subsequent-emerged sub-variants (>10 fold). The structures of rabbit ACE2 complexed with either SARS-CoV-2 prototype (PT) or Omicron BA.4/5 spike (S) proteins were determined, thereby unveiling the importance of rabbit ACE2 Q34 in RBD-interaction and elucidating the molecular basis of the enhanced binding with Omicron BA.4/5 RBD. These results address the highly enhanced risk of rabbits infecting SARS-CoV-2 Omicron sub-variants and the importance of constant surveillance.IMPORTANCEThe severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has swept the globe and caused immense health and economic damage. SARS-CoV-2 has demonstrated a broad host range, indicating a high risk of interspecies transmission and adaptive mutation. Therefore, constant monitoring for potential hosts is of immense importance. In this study, we found that Omicron BA.4/5 and subsequent-emerged sub-variants exhibited enhanced binding to both rabbit and hare angiotensin-converting enzyme 2 (ACE2), and we elucidated the structural mechanism of their recognition. From the structure, we found that Q34, a unique residue of rabbit ACE2 compared to other ACE2 orthologs, plays an important role in ACE2 recognition. These results address the probability of rabbits/hares being potential hosts of SARS-CoV-2 and broaden our knowledge regarding the molecular mechanism of SARS-CoV-2 interspecies transmission.

Defining a de novo non-RBM antibody as RBD-8 and its synergistic rescue of immune-evaded antibodies to neutralize Omicron SARS-CoV-2.

Currently, monoclonal antibodies (MAbs) targeting the SARS-CoV-2 receptor binding domain (RBD) of spike (S) protein are classified into seven classes based on their binding epitopes. However, most of these antibodies are seriously impaired by SARS-CoV-2 Omicron and its subvariants, especially the recent BQ.1.1, XBB and its derivatives. Identification of broadly neutralizing MAbs against currently circulating variants is imperative. In this study, we identified a "breathing" cryptic epitope in the S protein, named as RBD-8. Two human MAbs, BIOLS56 and IMCAS74, were isolated recognizing this epitope with broad neutralization abilities against tested sarbecoviruses, including SARS-CoV, pangolin-origin coronaviruses, and all the SARS-CoV-2 variants tested (Omicron BA.4/BA.5, BQ.1.1, and XBB subvariants). Searching through the literature, some more RBD-8 MAbs were defined. More importantly, BIOLS56 rescues the immune-evaded antibody, RBD-5 MAb IMCAS-L4.65, by making a bispecific MAb, to neutralize BQ.1 and BQ.1.1, thereby producing an MAb to cover all the currently circulating Omicron subvariants. Structural analysis reveals that the neutralization effect of RBD-8 antibodies depends on the extent of epitope exposure, which is affected by the angle of antibody binding and the number of up-RBDs induced by angiotensin-converting enzyme 2 binding. This cryptic epitope which recognizes non- receptor binding motif (non-RBM) provides guidance for the development of universal therapeutic antibodies and vaccines against COVID-19.

Structural basis of white-tailed deer, Odocoileus virginianus, ACE2 recognizing all the SARS-CoV-2 variants of concern with high affinity.

SARS-CoV-2 has been expanding its host range, among which the white-tailed deer (WTD), Odocoileus virginianus, became the first wildlife species infected on a large scale and might serve as a host reservoir for variants of concern (VOCs) in case no longer circulating in humans. In this study, we comprehensively assessed the binding of the WTD angiotensin-converting enzyme 2 (ACE2) receptor to the spike (S) receptor-binding domains (RBDs) from the SARS-CoV-2 prototype (PT) strain and multiple variants. We found that WTD ACE2 could be broadly recognized by all of the tested RBDs. We further determined the complex structures of WTD ACE2 with PT, Omicron BA.1, and BA.4/5 S trimer. Detailed structural comparison revealed the important roles of RBD residues on 486, 498, and 501 sites for WTD ACE2 binding. This study deepens our understanding of the interspecies transmission mechanisms of SARS-CoV-2 and further addresses the importance of constant monitoring on SARS-CoV-2 infections in wild animals. IMPORTANCE Even if we manage to eliminate the virus among humans, it will still circulate among wildlife and continuously be transmitted back to humans. A recent study indicated that WTD may serve as reservoir for nearly extinct SARS-CoV-2 strains. Therefore, it is critical to evaluate the binding abilities of SARS-CoV-2 variants to the WTD ACE2 receptor and elucidate the molecular mechanisms of binding of the RBDs to assess the risk of spillback events.

Seeing the T cell Immunity of SARS-CoV-2 and SARS-CoV: Believing the Epitope-Oriented Vaccines.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at the end of 2019 stimulated vigorous research efforts in immunology and vaccinology. In addition to innate immune responses, both virus-specific humoral and cellular immune responses are of importance for viral clearance. T cell epitopes play a central role in T cell-based immune responses. Herein, we summarized the peptide/major histocompatibility complex (pMHC) structures of the SARS-CoV-2-derived T cell epitopes available in the Protein Data Bank (PDB) and proposed the challenge and opportunities for using of T cell epitopes in future vaccine development efforts. A total of 27 SARS-CoV-2 related pMHC structures and five complexes with T cell receptors were retrieved. The peptides are mainly distributed on spike (S), nucleocapsid (N), and ORF1ab proteins. Most peptides are conserved among variants of concerns (VOCs) for SARS-CoV-2, except for several mutated peptides located in the S protein. The structures of human leukocyte antigen (HLA) complexed with seven epitopes derived from SARS-CoV were also retrieved, which showed a potential cross T cell immunity with SARS-CoV-2. Structural studies of antigenic peptides from SARS-CoV-2 and SARS-CoV help to visualize the processes and the mechanisms of cross T cell immunity. T cell epitope-oriented vaccines are potential next-generation vaccines for SARS-CoV-2, which are worthy of further investigation.

Broad protective RBD heterotrimer vaccines neutralize SARS-CoV-2 including Omicron sub-variants XBB/BQ.1.1/BF.7.

SARS-CoV-2 variants with severe immune evasion are a major challenge for COVID-19 prevention, especially the circulating Omicron XBB/BQ.1.1/BF.7 strains. Thus, the next-generation of broad-spectrum vaccines are urgently needed. Previously, we developed a COVID-19 protein subunit vaccine, ZF2001, based on the RBD-homodimer as the immunogen. To adapt SARS-CoV-2 variants, we developed chimeric RBD-heterodimers to induce broad immune responses. In this study, we further explored the concept of tandem RBD homotrimer and heterotrimer. Prototype SARS-CoV-2 RBD-homotrimer, prototype-Delta-BA.1 (PDO) RBD-heterotrimer and Delta-BA.2-BA.5 (DBA2BA5) RBD-heterotrimer were designed. Biochemical and cryo-EM structural characterization demonstrated total epitope exposure of the RBD-trimers. In mouse experiments, PDO and DBA2BA5 elicited broad SARS-CoV-2 neutralization. Potent protection against SARS-CoV-2 variants was observed in challenge assays and was correlated with neutralizing antibody titer. This study validated the design strategy of tandem RBD-heterotrimers as multivalent immunogens and presented a promising vaccine candidate, DBA2BA5, eliciting broad-spectrum immune responses, including against the circulating XBB/BF.7/BQ.1.1.

Structural basis for receptor binding and broader interspecies receptor recognition of currently circulating Omicron sub-variants.

Multiple SARS-CoV-2 Omicron sub-variants, such as BA.2, BA.2.12.1, BA.4, and BA.5, emerge one after another. BA.5 has become the dominant strain worldwide. Additionally, BA.2.75 is significantly increasing in some countries. Exploring their receptor binding and interspecies transmission risk is urgently needed. Herein, we examine the binding capacities of human and other 28 animal ACE2 orthologs covering nine orders towards S proteins of these sub-variants. The binding affinities between hACE2 and these sub-variants remain in the range as that of previous variants of concerns (VOCs) or interests (VOIs). Notably, R493Q reverse mutation enhances the bindings towards ACE2s from humans and many animals closely related to human life, suggesting an increased risk of cross-species transmission. Structures of S/hACE2 or RBD/hACE2 complexes for these sub-variants and BA.2 S binding to ACE2 of mouse, rat or golden hamster are determined to reveal the molecular basis for receptor binding and broader interspecies recognition.

Licorice-saponin A3 is a broad-spectrum inhibitor for COVID-19 by targeting viral spike and anti-inflammation.

Currently, human health due to corona virus disease 2019 (COVID-19) pandemic has been seriously threatened. The coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein plays a crucial role in virus transmission and several S-based therapeutic approaches have been approved for the treatment of COVID-19. However, the efficacy is compromised by the SARS-CoV-2 evolvement and mutation. Here we report the SARS-CoV-2 S protein receptor-binding domain (RBD) inhibitor licorice-saponin A3 (A3) could widely inhibit RBD of SARS-CoV-2 variants, including Beta, Delta, and Omicron BA.1, XBB and BQ1.1. Furthermore, A3 could potently inhibit SARS-CoV-2 Omicron virus in Vero E6 cells, with EC50 of 1.016 µM. The mechanism was related with binding with Y453 of RBD determined by hydrogen-deuterium exchange mass spectrometry (HDX-MS) analysis combined with quantum mechanics/molecular mechanics (QM/MM) simulations. Interestingly, phosphoproteomics analysis and multi fluorescent immunohistochemistry (mIHC) respectively indicated that A3 also inhibits host inflammation by directly modulating the JNK and p38 MAPK pathways and rebalancing the corresponding immune dysregulation. This work supports A3 as a promising broad-spectrum small molecule drug candidate for COVID-19.

A Simple and Affordable Method to Create Nonsense Mutation Clones of p53 for Studying the Premature Termination Codon Readthrough Activity of PTC124.

(1) Background: A premature termination codon (PTC) can be induced by a type of point mutation known as a nonsense mutation, which occurs within the coding region. Approximately 3.8% of human cancer patients have nonsense mutations of p53. However, the non-aminoglycoside drug PTC124 has shown potential to promote PTC readthrough and rescue full-length proteins. The COSMIC database contains 201 types of p53 nonsense mutations in cancers. We built a simple and affordable method to create different nonsense mutation clones of p53 for the study of the PTC readthrough activity of PTC124. (2) Methods: A modified inverse PCR-based site-directed mutagenesis method was used to clone the four nonsense mutations of p53, including W91X, S94X, R306X, and R342X. Each clone was transfected into p53 null H1299 cells and then treated with 50 µM of PTC124. (3) Results: PTC124 induced p53 re-expression in H1299-R306X and H1299-R342X clones but not in H1299-W91X and H1299-S94X clones. (4) Conclusions: Our data showed that PTC124 more effectively rescued the C-terminal of p53 nonsense mutations than the N-terminal of p53 nonsense mutations. We introduced a fast and low-cost site-directed mutagenesis method to clone the different nonsense mutations of p53 for drug screening.

De novo design of protein interactions with learned surface fingerprints.

Physical interactions between proteins are essential for most biological processes governing life1. However, the molecular determinants of such interactions have been challenging to understand, even as genomic, proteomic and structural data increase. This knowledge gap has been a major obstacle for the comprehensive understanding of cellular protein-protein interaction networks and for the de novo design of protein binders that are crucial for synthetic biology and translational applications2-9. Here we use a geometric deep-learning framework operating on protein surfaces that generates fingerprints to describe geometric and chemical features that are critical to drive protein-protein interactions10. We hypothesized that these fingerprints capture the key aspects of molecular recognition that represent a new paradigm in the computational design of novel protein interactions. As a proof of principle, we computationally designed several de novo protein binders to engage four protein targets: SARS-CoV-2 spike, PD-1, PD-L1 and CTLA-4. Several designs were experimentally optimized, whereas others were generated purely in silico, reaching nanomolar affinity with structural and mutational characterization showing highly accurate predictions. Overall, our surface-centric approach captures the physical and chemical determinants of molecular recognition, enabling an approach for the de novo design of protein interactions and, more broadly, of artificial proteins with function.

Deubiquitinase CYLD regulates excitatory synaptic transmission and short-term plasticity in the hippocampus.

The fate of proteins is determined by the addition of various forms of polyubiquitin during ubiquitin-mediated proteasomal degradation. Cylindromatosis (CYLD), a K63-specific deubiquitinase, is enriched in postsynaptic density fractions of the rodent central nervous system (CNS), but the synaptic role of CYLD in the CNS is poorly understand. Here we show that CYLD deficiency (Cyld-/-) results in reduced intrinsic hippocampal neuronal firing, a decrease in the frequency of spontaneous excitatory postsynaptic currents and a decrease in the amplitude of field excitatory postsynaptic potentials. Moreover, Cyld-/- hippocampus shows downregulated levels of presynaptic vesicular glutamate transporter 1 (vGlut1) and upregulated levels of postsynaptic GluA1, a subunit of the AMPA receptor, together with an altered paired-pulse ratio (PPR). We also found increased activation of astrocytes and microglia in the hippocampus of Cyld-/- mice. The present study suggests a critical role for CYLD in mediating hippocampal neuronal and synaptic activity.

Host range and structural analysis of bat-origin RshSTT182/200 coronavirus binding to human ACE2 and its animal orthologs.

Bat-origin RshSTT182 and RshSTT200 coronaviruses (CoV) from Rhinolophus shameli in Southeast Asia (Cambodia) share 92.6% whole-genome identity with SARS-CoV-2 and show identical receptor-binding domains (RBDs). In this study, we determined the structure of the RshSTT182/200 receptor binding domain (RBD) in complex with human angiotensin-converting enzyme 2 (hACE2) and identified the key residues that influence receptor binding. The binding of the RshSTT182/200 RBD to ACE2 orthologs from 39 animal species, including 18 bat species, was used to evaluate its host range. The RshSTT182/200 RBD broadly recognized 21 of 39 ACE2 orthologs, although its binding affinities for the orthologs were weaker than those of the RBD of SARS-CoV-2. Furthermore, RshSTT182 pseudovirus could utilize human, fox, and Rhinolophus affinis ACE2 receptors for cell entry. Moreover, we found that SARS-CoV-2 induces cross-neutralizing antibodies against RshSTT182 pseudovirus. Taken together, these findings indicate that RshSTT182/200 can potentially infect susceptible animals, but requires further evolution to obtain strong interspecies transmission abilities like SARS-CoV-2.

Cross-species recognition and molecular basis of SARS-CoV-2 and SARS-CoV binding to ACE2s of marine animals.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has an extremely broad host range that includes hippopotami, which are phylogenetically closely related to whales. The cellular ACE2 receptor is one of the key determinants of the host range. Here, we found that ACE2s from several marine mammals and hippopotami could efficiently bind to the receptor-binding domain (RBD) of both SARS-CoV and SARS-CoV-2 and facilitate the transduction of SARS-CoV and SARS-CoV-2 pseudoviruses into ACE2-expressing cells. We further resolved the cryo-electron microscopy complex structures of the minke whale ACE2 and sea lion ACE2, respectively, bound to the RBDs, revealing that they have similar binding modes to human ACE2 when it comes to the SARS-CoV-2 RBD and SARS-CoV RBD. Our results indicate that marine mammals could potentially be new victims or virus carriers of SARS-CoV-2, which deserves further careful investigation and study. It will provide an early warning for the prospective monitoring of marine mammals.

Broader-species receptor binding and structural bases of Omicron SARS-CoV-2 to both mouse and palm-civet ACE2s.

The Omicron variant of SARS-CoV-2 carries multiple unusual mutations, particularly in the receptor-binding domain (RBD) of the spike (S) protein. Moreover, host-adapting mutations, such as residues 493, 498, and 501, were also observed in the Omicron RBD, which indicates that it is necessary to evaluate the interspecies transmission risk of the Omicron variant. Herein, we evaluated the interspecies recognition of the Omicron BA.1 and Delta RBDs by 27 ACE2 orthologs, including humans. We found that Omicron BA.1 expanded its receptor binding spectra to palm-civet, rodents, more bats (least horseshoe bat and greater horseshoe bat) and lesser hedgehog tenrec. Additionally, we determined the cryo-electron microscopy (cryo-EM) structure of the Omicron BA.1 S protein complexed with mouse ACE2 (mACE2) and the crystal structure of Omicron RBD complexed with palm-civet ACE2 (cvACE2). Several key residues for the host range have been identified. These results suggest that surveillance should be enhanced on the Omicron variant for its broader-species receptor binding to prevent spillover and expansion of reservoir hosts for a prolonged pandemic.