How a SARS patient’s antibody binds to the COVID-19 virus

Researchers at the Scripps Research Institute and the University of Hong Kong have shown that a human antibody for the virus that causes severe acute respiratory syndrome (SARS) can also bind the new COVID-19-causing coronavirus (Science 2020, DOI: 10.1126/science.abb7269). The structural insights from this study might help in COVID-19 vaccine and drug design, the researchers say.

During a SARS epidemic in 2006, researchers isolated antibodies for the virus, SARS-CoV, from infected patients. Earlier this year researchers in China showed that one of those antibodies, CR3022, also binds to the spike protein of the virus that causes COVID-19, SARS-CoV-2 (Emerg. Microb. Infect. 2020 DOI: 10.1080/22221751.2020.1729069). To see how exactly the antibody binds to the spike protein, a group led by Ian A. Wilson ordered a sample of CR3022 and produced sections of the virus’s spike protein called the receptor binding domain (RBD).

The group used X-ray crystallography to find that, as predicted by the Chinese researchers, the antibody doesn’t bind where the RBD interacts with its human receptor. Instead, Wilson explains, the antibody latches onto a neighboring portion that only gets exposed when the protein changes structure as the virus infects a human cell.

“This is a very exciting study,” says Xavier Saelens, who is working to find antibodies against the novel coronavirus at the University of Ghent. The insights from this work could help researchers design an antibody to treat COVID-19. But Wilson also says vaccine developers could try and mimic that hidden structure so that the body produces its own antibodies against SARS-CoV-2. “There’s lots and lots of experience now at using structural information to try to design a vaccine that will actually target those particularly vulnerable sites,” he explains.

Wilson’s team found that the domain targeted by antibody CR3022 is similar in the SARS-causing virus and the new coronavirus. But Saelens notes one difference: the RBD of SARS-CoV has a glycosylation site, but SARS-CoV-2 does not. Saelens thinks that this small difference might be why CR3022 binds less tightly to the SARS-CoV-2 RBD than to the SARS-CoV one.

Wilson thinks there might be antibodies out there that target the same section more strongly. Or even antibodies that can effectively neutralize both viruses.

Wilson is now on the lookout for such dual-purpose antibodies, and people who have recovered from COVID-19 are offering to help. “It’s unbelievable the number of people in the public who are actually offering to provide samples” of antibodies their bodies have produced to SARS-CoV-2, he says. “I don’t know how many emails I’ve had over the weekend.” Short term, he says, the goal is to find good antibodies against the current virus, but longer term he hopes this work might help develop a vaccine that protects against related coronaviruses.

“You never know when the next virus is going to appear,” Wilson says “And so it’s always good to look for broad protection.”