In the realm of emerging infectious diseases, arenaviruses have long posed a formidable challenge due to their ability to cause severe hemorrhagic fevers with high lethality. Belonging to the Arenaviridae family, these viruses have drawn significant scientific attention as their outbreaks remain difficult to control and treat, primarily because of the absence of targeted antiviral therapies or vaccines. Despite decades of research, much of the molecular understanding has centered on the “Old World” arenaviruses, such as Lassa virus, leaving the “New World” counterparts, including the Sabiá virus—a pathogen endemic to South America and known to cause Brazilian hemorrhagic fever—largely enigmatic. A groundbreaking new study published in Nature Microbiology now elucidates the structural mechanics behind the Sabiá virus’s viral spike complex, shedding critical light on how these viruses engage host cells and initiate infection.
At the heart of arenavirus infectivity lies the spike complex, a sophisticated glycoprotein assembly protruding from the viral envelope. This complex is indispensable for mediating viral attachment to cellular receptors and facilitating membrane fusion, ultimately enabling the virus to release its genetic material into host cells. Though the spike structures of Old World arenaviruses have been resolved through advanced imaging, a gap has persisted in our understanding of New World arenavirus spikes, where sequence variation and structural differences could underpin distinct viral behaviors. Addressing this gap, Cohen-Dvashi, Katz, and Diskin employed single-particle cryo-electron microscopy (cryo-EM) to capture high-resolution images of the isolated spike complex of the Sabiá virus, achieving unprecedented clarity at resolutions of 2.6 and 2.9 angstroms for two distinct conformational states.
The researchers uncovered two primary conformations representing critical phases of the viral entry process. The first, a “closed” state, approximates the native, pre-fusion configuration of the spike complex. This closed form is characterized by a tightly packed assembly that appears to shield key fusion machinery elements from premature activation and immune recognition. Achieving 2.6 Å resolution, the detailed architecture revealed intricate folding patterns and glycosylation sites that likely contribute both to stability and immune evasion. The second conformational snapshot depicts an “open” state at 2.9 Å resolution, corresponding to a transient intermediate that the spike assumes during membrane fusion and cellular entry. This distinction between closed and open states illuminates the dynamic structural rearrangements necessary for the virus to effectively invade host cells.
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A novel finding of this study is the dependence of the spike’s conformational shifts on two critical environmental cues encountered during infection: acidic pH and the presence of a metal ion. Sabiá virus, like other enveloped viruses, exploits the acidic milieu within host endosomes to trigger conformational changes necessary for fusion. The data reveal that a yet unidentified metal ion stabilizes the open conformation, facilitating exposure of the fusion peptide and promoting membrane merger. This metal-dependent modulation suggests a uniquely intricate mechanism of viral entry, contrasting with previously characterized arenaviruses that do not appear to rely on such cofactors. Identifying this metal ion could present new avenues for therapeutic intervention by targeting viral entry pathways.
Intriguingly, these new structural insights hint at broader evolutionary and functional divergences within arenavirus clades. While Old World arenaviruses and New World clade C viruses share several conserved features in their spike complexes, clade B arenaviruses—including Sabiá—demonstrate distinct structural rearrangements modulated by metal binding and pH sensitivity. This functional divergence may reflect adaptation to different reservoirs and transmission cycles, potentially accounting for variations in pathogenicity and host range. Understanding these distinctive features enhances our grasp of arenavirus biology and highlights the necessity to consider clade-specific mechanisms when designing antiviral strategies.
The application of cryo-EM proved essential in visualizing these delicate conformations without introducing artifacts inherent to crystallography. By flash-freezing isolated spikes and capturing thousands of particle images, the team reconstructed three-dimensional models that elucidate subtle shifts within the glycoprotein domains. Notably, these structures provide direct visualization of receptor-binding sites, fusion loops, and the interplay of subunits that orchestrate entry. The precision of the 2.6 and 2.9 Å maps allowed identification of key amino acid residues involved in receptor engagement and structural stability, offering targets for future drug design.
Beyond characterizing static structures, the authors explored the biochemical triggers underlying the transition between closed and open states. Experiments revealed that lowering pH alone induced partial conformational changes but was insufficient to fully open the spike. Only in the presence of a specific metal ion did the spike adopt the fully open conformation necessary for membrane fusion. This nuanced interplay suggests a sophisticated viral strategy that ensures fusion only occurs within precise intracellular compartments, minimizing premature activation and improving infectivity. The identity of the metal ion remains elusive, but common candidates include divalent cations such as calcium, magnesium, or manganese, necessitating further biochemical probing.
This study also underscores the potential for metal ion chelators or pH-modifying agents as adjunctive therapies to disrupt Sabiá virus entry. By interfering with metal binding or local pH conditions, pharmacological agents could lock the spike complex in an inactive conformation, preventing fusion. Such strategies hold promise given the current absence of approved antivirals targeting New World arenaviruses. Moreover, the molecular details generated here enable rational design of fusion inhibitors or neutralizing antibodies aimed at structurally conserved or functionally critical regions of the spike.
Considering the broader implications, these findings could inform vaccine development efforts by pinpointing antigenic sites that elicit potent immune responses. The conformational states characterized reveal epitopes that are either exposed or hidden depending on the spike’s configuration, guiding immunogen design for maximal efficacy. Additionally, understanding the mechanisms of viral entry sheds light on how Sabiá virus and related arenaviruses evade host immunity during early infection stages, explaining the rapid progression and high mortality associated with hemorrhagic fever cases.
From a public health perspective, the enhanced understanding of Sabiá virus’s molecular biology is timely. South America remains a hotspot for emerging arenaviruses, driven by ecological changes and human encroachment into wildlife habitats. Enhanced surveillance combined with molecular characterizations like this one are crucial for preparedness and response to future outbreaks. The metal-dependent entry mechanism might also serve as a biomarker for rapid diagnostics or risk assessment.
The meticulous structural work by Cohen-Dvashi and colleagues opens avenues for targeted research into arenavirus fusion inhibitors. Such inhibitors, which have revolutionized treatment in other viral diseases like HIV and influenza, could be next-generation tools against hemorrhagic fever viruses. Moreover, the unique metal-ion dependency points to potentially exploitable vulnerabilities that differ from other arenavirus clades, emphasizing the value of tailored therapeutic approaches rather than one-size-fits-all solutions.
In summary, this study significantly advances our molecular fascination of arenaviruses by delivering the first detailed structural portrayal of the spike complex from the New World Sabiá virus. The identification of two distinct functional conformations—closed and open—and their regulation by acidic pH in conjunction with an unidentified metal ion enrich our understanding of viral entry in these deadly pathogens. As structural virology intersects with biochemistry and cellular biology, these insights promise to stimulate innovative countermeasures against arenavirus-induced hemorrhagic fevers that continue to threaten global health.
Further research is warranted to identify the specific metal ion implicated, to validate the findings in the context of intact virions and infected cells, and to explore the potential of small molecules or antibodies to interrupt the spike’s activation pathway. This work not only elevates the Sabiá virus onto the structural virology stage but also inspires renewed efforts to combat New World arenavirus threats through precision medicine grounded in atomic-level characterization.
Subject of Research: Structural characterization of the Sabiá virus spike complex and its metal-dependent conformational changes during viral entry.
Article Title: Metal-induced conformational changes in the Sabiá virus spike complex.
Article References:
Cohen-Dvashi, H., Katz, M. & Diskin, R. Metal-induced conformational changes in the Sabiá virus spike complex. Nat Microbiol (2025). https://doi.org/10.1038/s41564-025-02075-8
Image Credits: AI Generated
Tags: antiviral therapies for arenavirusesarenavirus infectivityBrazilian hemorrhagic feveremerging infectious diseasesglycoprotein assembly in viruseshemorrhagic fevers researchhost cell engagement by virusesNature Microbiology study on arenavirusesNew World arenavirusesSabiá virus spike complexstructural biology of virusesviral attachment mechanisms
