NIAID Now | February 19, 2020
The atomic-level structure of the SARS-CoV-2 spike protein in its prefusion conformation. The receptor binding domain, the part of the spike that binds to the host cell, is colored green.
NIAID scientists working with investigators from the University of Texas at Austin (UT) identified the atomic structure of an important protein on the surface of the novel coronavirus (SARS-CoV-2, formerly called 2019-nCoV). The findings appear in the peer-reviewed journal Science. The authors note that the findings will aid in the design of candidate vaccines and the development of treatments for COVID-19, the disease caused by the new virus, which was first identified in China in December 2019.
Like other coronaviruses, SARS-CoV-2 particles are spherical and have mushroom-shaped proteins called spikes protruding from their surface, giving the particles a crown-like appearance. The spike binds and fuses to human cells, allowing the virus to gain entry. However, coronavirus infection can be prevented or slowed if this process is disrupted.
Scientists in China shared the genome of a SARS-CoV-2 virus isolate to a global database, which NIAID and UT experts used to start their work determining the spike structure. The spike undergoes a massive rearrangement as it fuses the virus and cell membranes. The researchers confirmed that the original spike stabilized in its prefusion conformation is more likely to preserve targets for infection-blocking antibodies induced by a vaccine.
Importantly, the new data supports NIAID’s approach to a gene-based vaccine for COVID-19 and will also be useful in other vaccine approaches including protein-based vaccines and other nucleic acid or vector-based delivery approaches. NIAID scientists designed the stabilized spike antigen based on previous knowledge obtained from studying other coronavirus spike structures. NIAID and the biotechnology company Moderna, based in Cambridge, Massachusetts, are developing a messenger RNA (mRNA) vaccine, which directs the body’s cells to express the spike in its prefusion conformation to elicit an immune response.
The new research also confirms that the structure of the SARS-CoV-2 spike is very similar to that of the coronavirus responsible for the global outbreak of severe acute respiratory syndrome in 2003 that was eventually contained (known as SARS-CoV). However, despite the similarities, the paper shows that some monoclonal antibodies developed to target SARS-CoV do not bind to the new coronavirus, indicating that antibodies that recognize the SARS-CoV from 2003 will not necessarily be effective in preventing or treating COVID-19, the disease caused by the new virus.
Recent reports show that the novel virus and SARS-CoV also bind to the same receptor on the host cell. However, NIAID and UT scientists determined that SARS-CoV-2 binds more easily to this receptor as compared to SARS-CoV, which could potentially explain why SARS-CoV-2 appears to spread more efficiently from human-to-human. However, more data is needed to investigate this possibility, the authors note.
This research was supported by the NIAID Intramural Research Program and a NIAID grant to the University of Texas at Austin (R01-AI127521).
Reference:
D. Wrapp, N Wang et al. Cryo-EM Structure of the 2019-nCoV Spike in the Prefusion Conformation. Science DOI: 10.1126/science.abb2507 (2020)