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     Quick Explanation


    Core finding
    This Nature Microbiology study shows that a subset of genetically diverse HKU25 clade merbecoviruses use ACE2 (not DPP4) as a functional receptor, supported by multi-species ACE2 binding/entry assays and 2.5–2.7 Γ… cryo-EM structures of ACE2–RBD complexes that reveal determinants of orthologue selectivity, plus inhibitor/antibody sensitivity and an EjCoV-3 lineage with broad ACE2 usage and weak hACE2 entry.
    Evidence:



     Long Explanation


    Paper Review (critical, evidence-based): HKU25 clade MERS-related coronaviruses use ACE2 as a functional receptor
    Published: 30 Oct 2025 β€’ DOI: 10.1038/s41564-025-02152-y
    Claim assessed: HKU25 clade merbecoviruses use ACE2 (not DPP4) as a functional receptor, with structural determinants of orthologue selectivity and partial/weak human ACE2 compatibility in a subset (notably EjCoV-3).
    Figure 1 β€” Affinity snapshot (BLI, soluble ACE2 ectodomains)
    The study reports BLI K_D,app values of 130 nM (HsItaly2011 RBD ↔ R. norvegicus ACE2), 1.765 Β΅M (VsCoV-a7 RBD ↔ E. fuscus ACE2; shown as 1765 nM), and 532 nM (HKU25-462 RBD ↔ E. fuscus ACE2), while detecting no binding of soluble dimeric hACE2 ectodomain to these RBDs under their conditions.
    Figure 2 β€” Which evidence types converge on β€œACE2 is functional”?
    This study’s receptor conclusion is not based on a single assay. It combines orthologue-wide binding, orthologue-wide entry, kinetics, atomic structures, and functional mapping of ACE2 regions/glycans plus inhibition/neutralization data.
    What the paper does especially well (mechanistic credibility)
    • Structural + functional linkage: cryo-EM structures of ACE2–RBD complexes are used to motivate interface remodeling and glycan-mediated effects, then tested via ACE2 mutants/chimeras and binding/entry assays.
    • Receptor selectivity is mapped, not hand-waved: determinants include ACE2 segments (1–100 and 301–400) and nearby N-glycans that act as host-tropism barriers in their model system.
    • Assay design addresses receptor confusion: they explicitly contest previous reports proposing DPP4 engagement of the HKU25 clade by showing loss of detectable binding/entry to hDPP4 and DPP4 orthologues under their tested conditions.
    • Human adaptation assessed in an explicit subset: EjCoV-3 is highlighted as the only HKU25 strain among those tested that can use hACE2 for entry (though described as suboptimal/weak).
    Critical appraisal: limitations and β€œknown unknowns”
    • Incomplete coverage of HKU25 diversity: the paper reports that not all HKU25 clade members were confirmed to use ACE2 in the tested assays (e.g., VsCoV-1, VmSL2020, VmSL2021 were not confirmed). Therefore, ACE2 usage is strongly supported β€œfor the tested HKU25 subset,” while alternative receptor usage for other strains remains possible.
    • Cell-system constraints: binding and entry rely on heterologous expression of ACE2 orthologues and pseudovirus/rcVSV systems, which may not recapitulate all in vivo factors (protease landscape, membrane composition, accessory receptors). While inhibitors/entry-pathway experiments were performed, receptor usage in natural tissues still requires caution.
    • Affinity vs physiological relevance: BLI K_D,app values are reported for soluble ectodomains/constructs; real infection depends on full spike presentation, glycan processing, receptor membrane context, and multivalent avidity. The paper’s inhibitor and entry data help bridge this, but it’s still a modeling-to-phenotype gap that cannot be fully closed without in vivo infection data.
    • Glycan determinants are complex: the study identifies specific ACE2 glycans and residues near the interface and tests knock-in/knock-out effects. Yet N-glycosylation is host- and cell-context dependent; therefore, transferability of β€œglycan barriers” across tissue contexts is an open question.
    Figure 3 β€” Mechanistic β€œreceptor selection” model (as supported by their chimera/mutant mapping)
    Interpretation: the study identifies critical ACE2 determinants in two sequence regions (1–100 and 301–400) and finds that N-glycans proximal/within the interface modulate binding and entryβ€”often acting as tropism barriers for HKU25 clade viruses.
    Note: this plot is a qualitative support map (not raw measured values), created only to visually summarize which determinant classes the paper experimentally interrogated.
    Where the paper’s conclusions are strongest
    • Receptor identity (ACE2 vs DPP4) is experimentally tested using both binding and functional entry assays across orthologue panels, plus BLI and structural confirmation for representative strains.
    • Orthologue selectivity determinants are not just observed but mapped: ACE2 chimeras/mutants identify critical regions and glycans consistent with the structural interface.
    • Entry pathway logic (TMPRSS2 vs cathepsin B/L dependence) is experimentally supported via inhibitor sensitivity differing by cell type, rather than assumed universally.
    Figure 4 β€” Inhibition evidence: ACE2/S-targeting can block rcVSV-S propagation
    The paper reports potent inhibition by multiple strategies: TMPRSS2 inhibition (Camostat) and endolysosomal protease inhibition (E64d) show cell-type dependence; a fusion inhibitor (EK1C4) and S2-targeting antibodies (S2P6 and 76E1) block propagation/entry; and an hACE2-blocking antibody (h11B11) neutralizes rcVSVs bearing certain HKU25 spikes but not MERS-CoV (strain- and receptor-compatibility dependent).
    Note: this plot is qualitative (directional) because the prompt did not provide the full numerical IC50/neutralization table in machine-readable form.
    Paper review metrics (BGPT scoring)
    Novelty (1–10): 9
    Quality (1–10): 9
    Generality (1–10): 8
    Usefulness (1–10): 9
    Reproducibility (1–10): 9
    Explanatory depth (1–10): 9
    Scoring rationale is grounded in: (i) multi-assay evidence stack (binding, entry, kinetics, cryo-EM, mutational mapping, inhibition), (ii) direct structural validation of receptor engagement, and (iii) explicit acknowledgment of strain-level uncertainty and assay-context limitations.
    Actionable takeaways for the reader
    • Do not assume DPP4 for HKU25 clade receptor usage; this paper provides binding/entry/structure evidence for ACE2 (for the tested strains).
    • Look for ACE2 β€œcompatibility” barriers in regions 1–100 and 301–400 and in interface-proximal N-glycans; these are mechanistically mapped as tropism determinants.
    • EjCoV-3 is the β€œhuman ACE2” outlier in their experimental set, so it is a priority lineage for further receptor-context testing and surveillance inference.
    Further exploration via BGPT (beyond this review)


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    Updated: April 22, 2026

     BGPT Paper Review


    Study Novelty

    90%

    Novelty was estimated as very high because the study combines cross-species receptor panels, biophysical kinetics, and high-resolution cryo-EM to reassign HKU25 clade receptor usage toward ACE2 (rather than DPP4) and maps determinants (regions and glycans) mechanistically rather than inferentially. Evidence is directly supported within the paper’s multi-assay framework.


    Scientific Quality

    90%

    Estimated as high quality because it integrates structural biology (cryo-EM at ~2.5–2.7 Γ…), quantitative binding kinetics (BLI), and functional entry assays, plus causal determinant mapping through chimeras and targeted ACE2 glycan/residue edits. Main weaknesses are scope limitations for some HKU25 strains (not all confirmed), reliance on in vitro systems, and residual uncertainty about in vivo receptor context.


    Study Generality

    80%

    Generality is high because receptor usage and tropism determinants (including glycan-mediated selectivity) likely generalize to other merbecoviruses and contribute to broader frameworks for predicting zoonotic risk from spike/RBD receptor compatibility. It is slightly limited by strain-panel incompleteness and cell-system context dependence.


    Study Usefulness

    90%

    Usefulness is very high for virology preparedness because it provides actionable mechanistic determinants (ACE2 regions/glycans) and experimentally validated inhibition sensitivity for a set of ACE2-using HKU25 spikes, plus highlights EjCoV-3 as a lineage with broader ACE2 tropism.


    Study Reproducibility

    90%

    Reproducibility is high because methods are detailed (construct designs, receptor orthologue panel approach, BLI and cryo-EM workflows, pseudovirus/rcVSV systems, inhibitor assays), and cryo-EM maps/models are deposited with EMDB/PDB IDs.


    Explanatory Depth

    90%

    Explanatory depth is high because the paper links atomistic interface observations (cryo-EM) to specific ACE2 residue/glycan determinants through targeted mutagenesis/chimeras, and it ties receptor usage to functional entry and protease pathway activation.


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     Top Data Sources ExportMCP


     Analysis Wizard



    Summarizes reported ACE2 determinants (regions 1–100, 301–400, key N-glycan sites) into an interpretable scoring matrix and ranks ACE2 orthologue sequences likely to support HKU25 ACE2 engagement.



     Hypothesis Graveyard


    β€œAll HKU25 strains use ACE2” is no longer the best explanation because the paper reports that several HKU25 members were not confirmed to use ACE2 in the tested binding/entry conditions, implying either strain-specific receptor usage or context dependence.


    β€œACE2 vs DPP4 usage maps cleanly to viral species taxonomy” is less plausible because the study reports phylogenetic incongruities between whole-genome and S/RBD trees and shows receptor usage can deviate from genomic taxonomy/classification.

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