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Cryo-EM structure of the 2019-nCoV spike in the prefusion conformation

Why this mattered

This paper mattered because it made the SARS-CoV-2 spike protein structurally legible at the moment when the virus was becoming a global threat. By resolving the prefusion spike trimer at 3.5 Å, Wrapp and colleagues gave vaccine and antibody developers an experimentally grounded view of the viral surface protein most responsible for receptor binding, membrane fusion, immune recognition, and diagnostic targeting. The observation that one receptor-binding domain was in an “up,” ACE2-accessible state helped clarify how the spike samples conformations relevant to entry, while the measured higher ACE2 affinity relative to SARS-CoV spike supplied an early mechanistic clue for efficient human infection.

The paradigm shift was not that spike proteins were newly recognized as vaccine targets; coronavirus spike biology and prefusion-stabilization strategies already existed. Rather, the paper converted that prior platform knowledge into an immediately usable SARS-CoV-2 blueprint. Its structure validated the use of a prefusion-stabilized spike antigen and accelerated rational design, quality control, and interpretation of vaccine candidates, including the mRNA and viral-vector vaccines that soon followed. It also gave antibody researchers a map for asking which epitopes were conserved, which were novel, and why some SARS-CoV antibodies failed to bind the new virus.

In retrospect, the work became part of the structural biology infrastructure of the pandemic response. It linked viral genome release to atomic-scale antigen design in weeks, demonstrating how cryo-EM, protein engineering, and immunology could compress the timeline from pathogen identification to countermeasure development. Subsequent breakthroughs in neutralizing antibody discovery, variant mapping, structure-guided vaccine updates, and spike conformational studies all built on the same premise this paper made concrete: rapid structural determination of the key pathogen antigen can directly shape the medical response to an emerging infectious disease.

Abstract

The outbreak of a novel coronavirus (2019-nCoV) represents a pandemic threat that has been declared a public health emergency of international concern. The CoV spike (S) glycoprotein is a key target for vaccines, therapeutic antibodies, and diagnostics. To facilitate medical countermeasure development, we determined a 3.5-angstrom-resolution cryo-electron microscopy structure of the 2019-nCoV S trimer in the prefusion conformation. The predominant state of the trimer has one of the three receptor-binding domains (RBDs) rotated up in a receptor-accessible conformation. We also provide biophysical and structural evidence that the 2019-nCoV S protein binds angiotensin-converting enzyme 2 (ACE2) with higher affinity than does severe acute respiratory syndrome (SARS)-CoV S. Additionally, we tested several published SARS-CoV RBD-specific monoclonal antibodies and found that they do not have appreciable binding to 2019-nCoV S, suggesting that antibody cross-reactivity may be limited between the two RBDs. The structure of 2019-nCoV S should enable the rapid development and evaluation of medical countermeasures to address the ongoing public health crisis.

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