![]() There may be batch-to-batch variation.”īelow, an artists’ rendering of how the shape change of the spike protein drives the membrane fusion process, based on data from Chen’s team and other sources:Ĭhen’s many years of research on HIV have helped give his team a leg up on studying SARS-CoV-2. “If the protein is not stable, you may be able to induce antibodies, but they will be less effective in terms of blocking the virus. “We need to think about how to stabilize the spike protein,” he says. And this may limit their protective efficacy. Current vaccines that use the spike protein to stimulate the immune system may have varying mixes of the pre- and post-fusion forms, he says. Glycans are another feature that helps the virus avoid immune detection.Ĭhen believes his team’s findings have implications for vaccine development. The team was also surprised to find that the post-fusion spikes, similar to the pre-fusion spikes, have glycans, or sugar molecules, at evenly spaced locations on their surface. In effect, the post-fusion spikes may act as decoys that distract the immune system. The researchers speculate that having some spikes take the post-fusion form prematurely may also protect SARS-CoV-2 from our immune system, inducing antibodies that are non-neutralizing and ineffective in containing the virus. “We think the rigid structure of these post-fusion spikes protects the virus.” Evading immune detection “Most viruses don’t survive long outside the host,” Chen says. SARS-CoV-2 can carry both forms of the spike protein on its surface without needing to bind to the ACE2 receptor. That could explain why the virus appears to remain viable on various surfaces for hours to days. Chen suggests that being able to assume this alternate shape may help keep SARS-CoV-2 from breaking down, when it lands on a surface for example. The rigid “after” form protrudes slightly more from the virus surface. The second is ACE2 independent.” A coronavirus defense mechanism?Īs a result of the spontaneous shape change, coronavirus particles often bear both forms of the spike protein. “One is ACE2 dependent, and allows the virus to enter a host cell. “We propose that there are two routes for the conformational changes,” says Chen, in Boston Children’s Division of Molecular Medicine. Intriguingly, they also found that the spike can go from its original “before” shape into the “after” form prematurely, without the virus binding to a cell at all. Related: Sturdier spikes may explain SARS-CoV-2 variants’ faster spread: A mutation carried by the UK, South Africa, and Brazil SARS-CoV-2 variants stabilizes the spike protein, rendering the virus better able to infect us. In the “after,” post-fusion state, the protein assumes a rigid hairpin shape, they showed. Using the technique of cryogenic electron microscopy, Chen and colleagues established the molecular structure of the spike protein, both before and after fusion of the virus and cell membranes. The investigators, led by Bing Chen, PhD, believe these features may help SARS-CoV-2 hide from the immune system and survive longer in the environment. In the process, the study captured some surprise features in the “after” shape that may have implications for vaccine and therapeutic development. The two forms are published today in Science. A study led by Boston Children’s Hospital freeze-frames the spike protein for the first time in its “before” and “after” shapes. The spike protein is the main protein targeted by our antibodies and the protein used in most vaccines now in clinical trials. Knowing both shapes will aid in vaccine development.The second shape may help shield the virus from the environment and the immune system.Cryogenic electron microscopy freeze-frames SARS-CoV-2, the coronavirus behind COVID-19, before and after it changes shape.
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