Cryo-EM structures of #Měnglà virus GP reveal combined #Ebola- and #Marburg-like epitope masking strategies for #antibody evasion

 

Abstract

Ebola virus (EBOV) and Marburg virus (MARV) are highly lethal filoviruses that cause severe hemorrhagic fever in humans. A recently identified bat-borne filovirus, Měnglà virus (MLAV), uses the same NPC1 receptor as EBOV and MARV, raising concerns about its potential cross-species transmission. Here, we report cryo-EM structures of the MLAV surface glycoprotein (GP) in its unbound form and in complex with the MARV-neutralizing antibody MR191. MLAV GP exhibits distinctive structural features in the Wing and heptad repeat 1D (HR1D) regions, retains a visible Cap structure even after protease treatment, and contains a MARV GP-like α2 helix. MR191, a broadly neutralizing marburgvirus antibody that targets the conserved NPC1 receptor-binding pocket in MLAV GP, nonetheless exhibits impaired neutralizing activity, likely due to shielding by the MLAV Cap. In addition, the MLAV mucin-like domain, α2 helix, and HR1A region hinder binding by representative broadly neutralizing ebolavirus antibodies targeting the GP-waist, including 6D6, CA45, ADI-15878, and ADI-15946. Together, these results provide the first structural insights into MLAV GP and identify immune evasion driven by structural and sequence divergence as a major challenge for pan-filovirus antibody development.

Source: 

Link: https://www.pnas.org/doi/abs/10.1073/pnas.2529436123?af=R

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The #canine respiratory #epithelium is a permissive #ecosystem for #influenza interspecies #transmission and emergence

 

Abstract

The outcome of virus spillover ranges from dead-end infections to pandemics and is underpinned by host-pathogen interactions as well as evolutionary and epidemiological processes. The emergence of novel influenza A viruses (IAVs) has been associated with reassortment events involving multiple species, highlighting the importance of reservoir and intermediate hosts in viral emergence. Highly pathogenic H5N1 IAVs of the 2.3.4.4b genotype have caused a panzootic affecting a broad range of mammals. The role of dogs -arguably the most popular companion animal and a natural host of IAVs- in the ecology of IAVs under this new zooepidemiological scenario is unknown. To address this, we characterised the glycome of the dog respiratory epithelium, infected canine tracheal explants with multiple IAVs (including canine H3N2 and H3N8, equine H3N8, avian H3N8 and H5N1, swine H1N1, human H1N1 and H3N2, and bovine H5N1 viruses), and determined their cellular tropism. We show that the respiratory tract of dogs presents abundant sialylated glycans known to act as IAV receptors. Further, most IAVs (including 2.3.4.4b viruses) infected and replicated in dog tracheas, targeting mainly ciliated cells. Serological testing showed evidence of influenza spillover infections in dogs from the UK. Overall, our results show that the canine respiratory tract can provide a suitable environment for the generation of new IAVs. Given the multi-host contact networks of dogs in nature, they could act as recipients, bridging hosts, and/or mixing vessels for multiple IAV lineages, playing a central role in the ecology of influenza emergence.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

Medical Research Council, https://ror.org/03x94j517, MR/Y03368X/1, MC_UU_0034/2, MC_UU_0034/3

Biotechnology and Biological Sciences Research Council, BB/Y007093/1, BB/Y007298/1, BBS/E/PI/230001A, BBS/E/PI/230002A, BBS/E/PI/230002B, BBS/E/PI/230001C

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.06.04.730051v1

____

#SARS-CoV-2 #Omicron BA.2.86 and JN.1 expand #tropism in #human proximal #intestinal epithelium

 

Abstract

Omicron SARS-CoV-2 has diversified into multiple sub-lineages, complicating assessment of their intrinsic phenotypes due to background population immunity. We compare replication and biological characteristics of variants from BA.1 to JN.1 using human bronchial and lung explants, airway organoids, colon cells, and proximal intestinal enteroids. XBB.1.5 and EG.5.1 achieve higher replication titres in respiratory tissues than BA.2.86 and JN.1, indicating enhanced respiratory fitness. EG.5.1 displays dual cell-entry pathways and greater replication in alveolar epithelial cells, supporting increased lung tropism and pathogenicity. In contrast, BA.2.86 and JN.1 rely on TMPRSS2-mediated entry in airways. Notably, BA.2.86 and JN.1 replicate more efficiently than EG.5.1 in proximal intestinal enteroids in an ACE2- and TMPRSS2-dependent manner, but not in colon cells. JN.1 exhibits elevated intestinal tropism with limited proinflammatory cytokine induction, suggesting potential for faecal transmission. Here we show XBB.1.5 and EG.5.1 greater transmissibility and severity potential whereas BA.2.86 and JN.1 exhibit enhanced intestinal adaptation.

Source: 

Link: https://www.nature.com/articles/s41467-026-74111-y

____

G4 #Eurasian avian-like #H1N1 swine #influenza viruses exhibit enhanced #pathogenicity potential in mice and #pigs

 

Abstract

Currently circulating swine influenza viruses (SIVs) mainly include H1N1, H1N2, and H3N2 subtypes. In this study, two G4 genotype Eurasian avian-like (EA) H1N1 SIVs were isolated from 556 samples collected between 2023 and 2026. A systematic analysis was conducted on the two EA H1N1 isolates (FYD30 and YZF69) to assess their pandemic potential. The hemagglutinin (HA) proteins of both H1N1 viruses possessed residues 225E and 228S, indicating enhanced affinity for human-like alpha-2,6-linked sialic acid receptors, which was confirmed by receptor-binding assays. Polymerase activity tests demonstrated that the two SIVs exhibited significantly higher activity in mammalian cells, relative to avian cells, which is consistent with the efficient replication in mammalian cells. Challenge experiments revealed that both H1N1 caused significant pathogenicity in mice and pigs, with YZF69 exhibited higher virulence than FYD30. The higher virulence of YZF69 may be attributed to its molecular features, including the NP Q357K mutation, and an additional glycosylation site in HA. In conclusion, currently circulating EA H1N1 SIVs have acquired key molecular signatures of mammalian adaptation, exhibit enhanced virulence in mammals, and continue to undergo extensive reassortment driven by international swine trade. These findings highlight the potential pandemic risk of SIVs and underscore the urgent need for strengthened surveillance.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.12.724537v1

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A single PA-X #mutation in #bovine-origin #H5N1 #influenza virus reduces #pathogenicity in mice

 

Abstract

Dairy cows have emerged as a reservoir for human infection with highly pathogenic avian influenza (HPAI) H5N1. At the bovine-human interface, H5N1 strains may acquire adaptive mutations that influence their zoonotic potential. Sequence analysis identified a K142E substitution (bovine to human) in the PA and PA-X proteins, with the potential to affect both polymerase activity and host shutoff. Here, we used a loss-of-function approach to investigate how the bovine substitution (E142K) in PA/PA-X impacts viral replication, host shutoff activity, and pathogenicity in the human H5N1 background. Viral growth kinetics demonstrated that the virus containing the E142K substitution is attenuated, with reduced replication compared to wild-type (WT) virus. Consistently, PA-X-mediated host shutoff activity was reduced, resulting in increased induction of interferon (IFN) responses relative to WT. In vivo, mice infected with the E142K mutant virus survived, whereas infection with the WT virus was uniformly lethal. Despite comparable viral titers and inflammation score in mouse lungs, cytokine and chemokine profiling revealed distinct immune responses, with reduced CCL2 and increased CCL5 and IFN-γ in mice infected with the E142K mutant virus compared to mice infected with the WT virus. These findings indicate that increased virulence of the human-adapted strain is driven by a PA-X mutation that modulates inflammatory responses, producing distinct immune signatures linked to host survival or viral lethality rather than changes in polymerase activity by PA. Collectively, these results highlight PA-X as a key determinant of pathogenicity of H5N1 and a potential target for the rational design of antiviral strategies.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.09.724031v1

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#Genetic and #biological characterization of #H9N2 avian #influenza viruses isolated from #swine in #China

 

Abstract

Background

H9N2 avian influenza virus (AIV) has been circulating in poultry in China for decades and are undergoing adaptation to mammals, posing potential pandemic risks. To investigate the prevalence of H9N2 AIVs in swine, we conducted surveillance in Shandong Province from 2021 to 2023.

Results

Two H9N2 influenza virus strains, A/swine/Shandong/417/2021(Sw/SD/417/21) and A/swine/Shandong/662/2022 (Sw/SD/662/22), were successfully isolated from swine and genetically characterized. Phylogenetic analyses showed that both isolates were reassortants containing gene segments from multiple H9N2 AIV lineages and closely related to currently circulating H9N2 AIV. Key molecular marker analysis revealed that both isolates carried mammalian-adaptive residues in the HA receptor-binding sites (183 N, 190 V, 226 L), a novel HA cleavage site variant (PSKSSRGL), PB2 mutations (A588V, E627V), and the M2 S31N substitution, suggesting potential adaptation to mammalian hosts and resistance to adamantane antivirals. Mice infection experiments demonstrated efficient viral replication in the respiratory tract, particularly in the lungs, but only mild histopathological changes were observed, with no significant weight loss or mortality, indicating low pathogenicity in mice. Serological surveillance of 3,172 swine serum samples showed a low prevalence of H9N2 influenza virus infection (0.44%), with positive samples sporadically distributed across regions and years.

Conclusion

In summary, although H9N2 AIV infection in swine is rare and generally mild, the presence of mammalian-adaptive markers and reassortant genomes highlights the potential risk of cross-species transmission and subclinical adaptation. Continuous avian–swine–human influenza surveillance is therefore essential to mitigate the potential threat posed by H9N2 AIV.

Source: 

Link: https://link.springer.com/article/10.1186/s12917-026-05501-z

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Variable #transmission efficiency of #mammalian origin #HPAI D1.1 #H5N1 strains in #ferrets

 

Abstract

Highly pathogenic avian influenza H5N1 2.3.4.4b genotype D1.1 lineage continues to predominate in the United States wild bird population and has spilled over into dairy cattle three independent times. To assess the transmission risk of this sublineage, we performed direct-contact transmission experiments for three distinct D1.1 strains in ferrets. Two of these strains were isolated from humans and one from a lethal cat infection. We found that only one human isolate (A/NV/10/2025) was able to transmit efficiently between ferrets. Compared to the other strains, this isolate harbored the mammalian adaptive PB2 D701N mutation, suggesting this mutation may be critical for D1.1 transmission as opposed to the PB2 E627K substitution present in the lethal cat isolate. Based on these data we conclude that the transmission fitness of D1.1 strains is modest but that special attention should be paid to emergence of adaptation at the PB2 701 position.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

National Institute of Allergy and Infectious Diseases, https://ror.org/043z4tv69, 75N93021C00015, 75N93021C00017

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.07.722809v1

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Loss of nsp14-exonuclease activity impairs the #replication, proofreading, fitness, and #pathogenesis of #SARS-CoV-2

 

ABSTRACT

Coronaviruses (CoVs) replicate their RNA genomes with a higher degree of fidelity than other RNA viruses, a mechanism mediated by the proofreading and recombination activities of the exoribonuclease domain of replicase nonstructural protein 14 (nsp14-ExoN). Both murine hepatitis virus (MHV) and SARS-CoV tolerate nsp14-ExoN loss-of-function mutations (ExoN−) (D90A and E92A), but have impaired replication fidelity and pathogenesis; yet identical substitutions in MERS-CoV and SARS-CoV-2 have been reported to be lethal. Here, we report a saturation mutagenesis approach facilitating the recovery and analysis of several constellations of SARS-CoV-2 nsp14 ExoN-inactivating, loss-of-function substitutions, including the canonical D90A and E92A. Biochemical assays with purified WT or ExoN-nsp10-14 fusion proteins confirmed that active site substitutions abolished ExoN activity (ExoN−). SARS-CoV-2 ExoN− viruses exhibited impaired replication, RNA synthesis, and recombination, as well as decreased replication fidelity and loss of fitness in vitro. ExoN− viruses were significantly attenuated for replication in human primary airway epithelial cells and were attenuated for replication and pathogenesis in WT mice, as well as the highly susceptible K18 transgenic mice. In the absence of interferon signaling in vivo, SARS-CoV and SARS-CoV-2 ExoN− viral replication could be partially restored. These results demonstrate that SARS-CoV-2 ExoN− viruses are viable but highly impaired for replication, fitness, and fidelity in vitro, as well as innate immune antagonism and pathogenesis in vivo. Collectively, our results solidify the multiple critical roles of nsp14-ExoN across CoV genera and establish new approaches for rescuing and analyzing loss-of-function substitutions in studies of CoV replication, pathogenesis, and evolution.

Source: 

Link: https://journals.asm.org/doi/10.1128/mbio.00073-26

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Opposing #cell type preferences for binding and #replication shape #influenza A virus infection in #human #airways

 

Abstract

Influenza A viruses (IAVs) pose a persistent threat to human health through seasonal epidemics and zoonotic spillover from avian reservoirs. As respiratory pathogens, they primarily target the airway epithelium. However, it remains unclear how host cell-specific barriers jointly shape viral tropism and replication in primary human airway cultures. Here, we show that avian IAVs can infect ciliated and secretory cells but preferentially bind to ciliated cells, consistent with higher abundance of their receptor alpha2,3-linked sialic acids, specifically sialyl Lewis X glycans, present on the apical surface of ciliated cells. Replication levels were comparable between secretory and ciliated cells for the avian strains, resulting in an overall preference for ciliated cells. In contrast, human IAVs also preferentially bind to ciliated cells but independently of alpha2,6-linked sialic acid abundance. Human IAVs replicate more efficiently than avian IAVs due to their ability to utilize human ANP32 proteins, but they also exhibit cell type-specific differences due to ANP32, allowing for higher viral RNA levels in secretory cells. Thus, preferential binding to ciliated cells coupled with enhanced replication in secretory cells equalizes overall infection levels across cell types for human IAVs. Together, our findings highlight the spatiotemporal complexity and interplay of IAV infection dynamics in the airway epithelium and redefine current models of influenza A virus tropism.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

Swiss National Science Foundation, 310030_204166

UZH Candoc, FK-25-039

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.04.722582v1

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#Replication Efficiency of Contemporary Highly Pathogenic Avian #Influenza #H5N1 Virus Isolates in #Human #Nasal Epithelium Model

 

Abstract

Replication of influenza A virus in human nasal epithelium affects transmissibility and disease. We compared virus replication and immune responses in human nasal epithelium infected with seasonal and highly pathogenic avian influenza A(H5N1) viruses. Contemporary H5N1 viruses replicated better than the historical isolate; however, interferon response to B3.13 genotype viruses was dampened.

Source: 

Link: https://wwwnc.cdc.gov/eid/article/32/5/26-0053_article

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An #NS1-F161L #Substitution Determines #Host-Driven #Virulence Enhancement of #H5N6 Avian #Influenza Virus in #Ducks

 

Abstract

H5 subtype avian influenza virus (AIV) can infect both chickens and ducks, leading to substantial economic losses. Nevertheless, certain strains cause silent infections in ducks. In this study, a goose-origin clade 2.3.4.4h H5N6 AIV was isolated, which caused high mortality in mixed-gender white leghorn chickens but no deaths in mixed-gender mallard ducks. After independent serial in vitro passage in duck embryo fibroblasts (DEFs) and in vivo passage in specific-pathogen-free (SPF) ducks, the DEF-passage 10 (P10) virus induced markedly higher mortality rates and viral loads in SPF ducks compared to the DEF-P1 virus and the original parental virus prior to passage. Similarly, the in vivo-passaged P3 and P4 viruses exhibited significantly higher mortality rates than the P1 virus in SPF ducks, with 100% mortality and markedly increased viral titers in the organs. A whole-genome SNP analysis identified seven high-frequency mutations in the M1, NA and NS1 proteins. The NS1-F161L substitution virus exhibited significantly increased mortality rates, viral loads in multiple tissues, and a robustly induced innate immune response in ducks. Furthermore, dynamic evolutionary variations in the NS1 protein among global H5 avian influenza viruses revealed that the NS1-F161L substitution became dominant in clade 2.3.4.4b viruses in 2021 and subsequent years. Collectively, our findings demonstrate that host-driven adaptation can rapidly increase the pathogenicity of H5N6 AIVs in ducks and identify NS1-F161L as a critical virulence marker. These results offer novel insights relevant to the molecular surveillance, virulence prediction, and risk assessment of circulating H5 AIVs in waterfowl.

Source: 

Link: https://www.mdpi.com/1999-4915/18/5/488

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Heart-nosed #bat #alphacoronaviruses use #human CEACAM6 to enter #cells

 

Abstract

Identifying viruses with zoonotic potential on the basis of their ability to enter human cells is a critical component of pandemic prediction, prevention and preparedness. Here using a computational approach that retains maximum phylogenetic diversity, we selected an optimal subset of alphacoronavirus spike proteins to screen against broad coronavirus receptor libraries. Most of the selected spike proteins did not use any of the established coronavirus receptors. However, the pseudotyped spike protein of Cardioderma cor (heart-nosed bat) coronavirus KY43 (CcCoV-KY43) could enter human cells. Using a recombinant CcCoV receptor-binding domain (RBD) and a human receptor screening platform, we identified direct interactions with the human CEACAM proteins CEACAM3, CEACAM5 and CEACAM6. Overexpression of human CEACAM6—a protein widely expressed in the human lung—conferred permissivity to otherwise refractory human cells. A crystal structure showed that the RBD binds the amino-terminal IgV-like domain of human CEACAM6. Immune surveillance studies using sera of individuals from the Taveta region of Kenya, where CcCoV-KY43 was identified, did not show significant evidence of recent spillover. Wider characterization of alphacoronaviruses related to CcCoV-KY43 showed that human CEACAM6 is used by two other CcCoVs collected in Kenya. Moreover, there was more restricted nonhuman CEACAM6 tropism for viruses isolated from Rhinolophus bats from Russia and China. Thus, alphacoronaviruses that use CEACAM6 are probably geographically widespread, and viruses from East Africa show potential for transmission to humans.

Source: 

Link: https://www.nature.com/articles/s41586-026-10394-x

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A natural five-amino-acid insert at the S2’ #cleavage site of #MERS-CoV #spike enhances viral membrane fusion

 

Highlights

• A novel 5-aa insert, TSGVF, is present at the S2’ cleavage site of the spike protein of MERS-CoV from dromedary camels.

• Pseudovirus-based entry assays showed that the TSGVF insert increases viral entry efficiency in different human cells.

• Pseudovirus with TSGVF insert at the S2’ cleavage site showed strong resistance to TMPRSS2 inhibitor.

• The natural occurrence of TSGVF insert at the spike S2’ cleavage site enhances viral membrane fusion and syncytia formation.

Source: 

Link: https://www.sciencedirect.com/science/article/pii/S1995820X26000611?via%3Dihub

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#Infection of the #bovine mammary #gland by avian #H5N1 subclade 2.3.4.4b #influenza viruses

 

Abstract

The emergence of the panzootic clade of highly pathogenic avian influenza H5N1 (2.3.4.4b) in 2020 marked a major expansion in the host range of influenza A viruses (IAVs), raising concerns about further cross‑species transmission events and zoonotic spillover. Introduction of 2.3.4.4b viruses into U.S. dairy herds has resulted in widespread circulation, accompanied by reduced milk yield, mastitis, and high viral loads in milk. Notably, virus circulation in dairy cattle represents a novel route for mammalian adaptation and transmission that has already led to more than 40 human cases in the U.S. since 2024. Here, we investigated whether avian clade 2.3.4.4b viruses could infect mammary tissue from Aberdeen Angus, Holstein Friesian, and Limousin cattle, three breeds commonly farmed in Europe, the Americas, and Oceania. Using mammary gland explants, we inoculated tissues with attenuated reassortant viruses expressing the haemagglutinin and neuraminidase glycoproteins of three 2.3.4.4b viruses that predated the emergence of H5N1 in US cattle: A/chicken/England/053052/2021 (AIV07), A/chicken/Scotland/054477/2021 (AIV09), and A/chicken/England/085598/2022 (AIV48). Infected epithelial cells were identified using immunohistochemistry in explants from both the teat and gland cistern for all three breeds following infection with AIV09 and AIV48, indicating that mammary tissue from each of the three tested cattle breeds cattle is permissive to H5N1 infection. Lectin staining showed expression of both α2,3‑linked and α2,6‑linked sialic acids in the mammary tissue of all donors showing that all three breeds have the potential to support infection with both avian-adapted and mammalian adapted IAVs. Together, these findings demonstrate that mammary glands from both beef and dairy cattle breeds are permissive to infection with avian‑adapted and mammalian-adapted H5N1 viruses and highlight the potential for this tissue to act as a mixing vessel for IAV reassortment, underscoring the need to include cattle in ongoing H5N1 surveillance and risk‑assessment frameworks.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

Medical Research Council, https://ror.org/03x94j517, MR/Y03368X/1, MR/Y03368X/1, MC_UU_0034/2, MC_UU_0034/3, MC_UU_0034/1

Biotechnology and Biological Sciences Research Council, https://ror.org/00cwqg982, BB/V004697/1

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.04.16.718897v1

____

Acquisition of specific #human respiratory tract binding of 2.3.4.4b #H5N1 #hemagglutinins requires multiple #mutations

 

Abstract

It has been suggested that the hemagglutinin of the human-infecting cattle-derived 2.3.4.4b virus A/Texas/34 (H5TX) requires only one mutation, namely Q226L, to switch from binding avian-type to human-type receptor preference. In this study, we examined the binding of H5TX Q226L, along with other key mutations, to sections of human trachea. We conclude that, while H5TX Q226L can bind human-type receptors, more than a single mutation is required for this protein to bind to human respiratory tract tissue. We also report changes in receptor-binding specificity of another 2.3.4.4b HA mutant, H5FR Q226L, associated with the presence of a multibasic cleavage site. This study offers insight into the determinants of evolution towards human-type receptor binding in currently circulating H5Nx viruses. It also emphasizes the importance of testing individual strains using additional methods, including tissue-based approaches, alongside synthetic glycans.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

NWO, OCENW.M20.106

Horizon, 862605

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.04.16.718875v1

____

#SARS-CoV-2 and #MERS-CoV disrupt #host #protein synthesis via nsp1 with differential effects on the integrated stress response

 

Significance

Coronaviruses cause disease across a wide range of animal species and the human coronaviruses SARS-CoV-2 and MERS-CoV have caused epidemics of severe respiratory illness. Thus, it is imperative to understand how these viruses antagonize host responses and cause lethal disease. We show here that the betacoronavirus nonstructural protein 1 (nsp1) promotes shutdown of host protein synthesis while preserving viral protein synthesis and, in addition, promotes degradation of host mRNAs. However, SARS-CoV-2 and MERS-CoV differ in their ability to manipulate the host integrated stress response, indicating that it is important to understand detailed coronavirus–host interactions and how they differ even between lethal coronaviruses. Such insights will inform the development of antiviral therapeutics to treat and prevent current and future coronavirus outbreaks.

Abstract

Coronaviruses pose a serious threat to public health, driving the need for antiviral therapeutics and vaccines. Therefore, it is paramount to understand how this family of viruses evades cellular antiviral responses and establishes productive infection. The conserved coronavirus nonstructural protein 1 (nsp1) has been shown to inhibit host protein synthesis and, in some coronaviruses, promote host messenger RNA (mRNA) degradation while viral mRNAs are protected. We showed previously that severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) induces activation of host integrated stress response (ISR) kinases protein kinase R (PKR) and PKR-like endoplasmic reticulum kinase (PERK), which promote phosphorylation of eukaryotic initiation factor 2 (eIF2α) and consequent inhibition of host protein synthesis. In contrast, eIF2α remains unphosphorylated during Middle East respiratory syndrome coronavirus (MERS-CoV) infection. To investigate the interactions of nsp1 and the ISR kinases, we utilized recombinant SARS-CoV-2 and MERS-CoV expressing nsp1 with mutations in each of two conserved domains. Upon infection with SARS-CoV-2 nsp1 mutants, translation was shut down in wildtype (WT) and PKR knockout (KO) cells but rescued in PERK KO cells, likely due to reduced p-eIF2α. In contrast, translation was rescued during infection with the analogous MERS-CoV nsp1 mutants even in WT cells. Moreover, SARS-CoV-2 WT suppressed expression of GADD34, a negative regulator of eIF2α phosphorylation, while SARS-CoV-2 nsp1 mutants induced GADD34. In contrast, MERS-CoV WT induced GADD34. Utilizing single-molecule fluorescence in situ hybridization, we found that SARS-CoV-2 and MERS-CoV nsp1 promote host mRNA degradation during WT, but not nsp1 mutant, infection. Thus, SARS-CoV-2 and MERS-CoV differ in interactions with the ISR and nsp1 control of host protein synthesis.

Source: 

Link: https://www.pnas.org/doi/abs/10.1073/pnas.2536296123?af=R

____

Historical #Pandemic and Contemporary #Influenza A Viruses Reveal #PB2 M631L as a Convergent #Adaptation to #Human ANP32

 

Abstract

Understanding the genetic changes that allow avian influenza A viruses (IAVs) to switch their natural hosts and establish productive infection in humans is important for pandemic risk assessment. Adaptations in the IAV polymerase are required to overcome species-specific restrictions imposed by host ANP32 proteins. Notably, avian virus polymerase is generally only poorly supported by human ANP32 proteins due to species-specific differences. Consequently, efficient polymerase adaptation to the binding interface of human ANP32 requires distinct amino acid changes, such as PB2 E627K. A separate adaptation, PB2 M631L, has recently been reported in mammalian-adapted IAV; however, its functional role across divergent viral lineages and its relationship to host ANP32-dependent adaptation remain incompletely defined. Here, we examine PB2 M631L in the polymerases of a 1918 pandemic strain, a recombinant contemporary H1N1pdm09, and a recent clade 2.3.4.4b H5N1 virus. Using polymerase activity and protein-interaction assays, we show that PB2 M631L enhances polymerase activity and ANP32 binding in human—but not avian—contexts, and that this effect is conserved across multiple viral backgrounds. In H1N1pdm09, PB2 M631L also increased virus replication in mammalian cells. These findings indicate that PB2 M631L contributes to enhanced polymerase compatibility with human ANP32 proteins and are consistent with a role in adaptation across multiple influenza virus lineages. Our results highlight how analysis of historical pandemic strains can inform risk assessment for future emerging viruses.

Source: 

Link: https://www.mdpi.com/2076-2607/14/4/859

____

#Species - and #variant - specific #ACE2 compatibility shapes #SARS-CoV-2 #spillover potential in North American #cervids

 

Abstract

Free-ranging white-tailed deer (WTD) are established SARS-CoV-2 reservoirs, but the susceptibility of other cervid species remains unclear. Here we integrate receptor analysis, structural modeling, and field surveillance to assess SARS-CoV-2 susceptibility across North American cervids. We identify species- and variant-specific differences in ACE2–spike compatibility. Elk ACE2 exhibits weak binding to the ancestral strain (Wuhan-Hu-1) and Delta spike receptor-binding domains (RBDs), likely due to a unique K31N substitution. In contrast, it shows stronger binding to Alpha, Beta, Gamma, and Omicron RBDs containing N501Y. Biophysical assays, gel filtration chromatography, and cryo-EM confirm stable complex formation between elk ACE2 and Alpha RBD, but not RBD from the ancestral strain. Despite weak binding, elk ACE2 supports viral entry and replication in vitro. However, surveillance revealed limited evidence of infection in the United States, contrasting with widespread WTD transmissions. These findings demonstrate that ACE2 compatibility alone is insufficient to predict reservoir potential and provide a framework for assessing species susceptibility to emerging coronaviruses.

Source: 

Link: https://www.nature.com/articles/s41467-026-71623-5

____

#Genetic and #biological characterization of a #duck-origin clade 2.3.4.4b #H5N6 avian #influenza virus reveals partial #mammalian #adaptation

 

Highlights

• Duck-origin H5N6 virus A/Duck/Jiangsu/628/2022 shares high homology with the human strain A/Yangzhou/125/2022.

• The 628 strain shows mammalian adaptation markers: HA mutations enhance human receptors affinity and NA mutations reduce sensitivity to neuraminidase inhibitors.

• Limited airborne transmission but detectable droplet-mediated spread suggests increased mammalian transmission risk.

Abstract

Clade 2.3.4.4b H5Nx highly pathogenic avian influenza viruses (HPAIVs) have caused extensive outbreaks in poultry worldwide. H5 HPAIVs have caused sporadic but severe human infections in China, representing a persistent zoonotic threat. Here, we identified a duck-origin H5N6 HPAIV (A/Duck/Jiangsu/628/2022) through routine surveillance and assessed its biological characteristics and mammalian pathogenesis. Phylogenetic analysis revealed > 98% nucleotide identity between strain 628 and the concurrent human H5N6 strain A/Yangzhou/125/2022. Molecular characterization identified multiple mammalian adaptation markers: hemagglutinin substitutions (S137A, T160A, T192I) associated with enhanced human receptor binding; neuraminidase mutations (I117T, D198N) linked to reduced neuraminidase inhibitor susceptibility; and polymerase complex changes (PB1-D622G, PA-K142Q) conferring increased mammalian cell replication. In vitro studies demonstrated that 628 virus replicated more efficiently in mammalian than in avian cells and exhibited dual receptor-binding specificity. Mouse pathogenicity assays revealed moderate virulence with progressive lung pathology. Critically, transmission experiments confirmed both direct contact and airborne transmission capabilities of 628 in guinea pigs. These findings demonstrate that circulating H5N6 viruses have acquired partial mammalian adaptation while retaining avian fitness, significantly elevating pandemic potential. Enhanced surveillance of wild bird populations, poultry farms, and live poultry markets is urgently needed to develop effective prevention and control strategies.

Source: 

Link: https://www.sciencedirect.com/science/article/abs/pii/S037811352600146X?via%3Dihub

____

Q1020R in the #spike proteins of #MERS-CoV from Arabian #camels confers resistance against soluble #human #DPP4

 

ABSTRACT

The Middle East respiratory syndrome coronavirus (MERS-CoV) is a pre-pandemic coronavirus that is transmitted from camels, the natural reservoir, to humans and can cause severe disease. MERS cases have been documented in Arabia but not Africa, although the virus is circulating in both Arabian and African camels. Further, evidence has been provided that viruses in African camels might have a reduced capacity to cause disease. However, the underlying determinants are incompletely understood. Here, employing pseudotyped particles as model systems for MERS-CoV entry into cells, we compared cell entry of viruses from African and Arabian camels and its inhibition. We show that viruses found in Arabian camels and recent human cases are less susceptible to inhibition by human soluble DPP4 (sDPP4) than viruses from African camels, although both enter human cells efficiently and are comparably sensitive to inhibition by interferon-induced transmembrane (IFITM) proteins and neutralizing antibodies. Furthermore, relative resistance to sDPP4 was linked to mutation Q1020R, present in the spike proteins of recent Arabian but not African viruses. Finally, indirect evidence was obtained that sDPP4 in human plasma can inhibit MERS-CoV cell entry. These results support the concept that soluble DPP4 might constitute a natural barrier against human infection that is more efficiently overcome by viruses currently circulating in Arabian camels than those in African camels.

Source: 

Link: https://journals.asm.org/doi/10.1128/jvi.00282-26

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