Sugar-like molecules on the surface of the novel coronavirus create a "kind of protective coat" that hides it from the host's neutralising antibodies, according to a study that may help develop new vaccines and therapeutics against COVID-19. Using ultra-high resolution microscopy techniques, researchers from the Max Planck Institute of Biophysics in Germany, assessed the surface structure of the novel coronavirus and found that its entire spike protein (S), which enables it to enter host cells, is covered with chains of sugar-like molecules called glycans.
The findings, published in the journal Science, noted that the globular portion of the spike protein, which contains the machinery needed for the virus to fuse with host cells, is connected to a flexible stalk.
"We show that the stalk domain of S contains three hinges, giving the head unexpected orientational freedom.
We propose that the hinges allow S to scan the host cell surface, shielded from antibodies by an extensive glycan coat," the scientists wrote in the study.
According to the researchers, the study's findings about the stalk, which fixes the globular part of the spike protein to the virus surface, are new.
They identified three joints in the spike protein -- hip, knee, and ankle -- that give the stalk its flexibility.
"The stalk was expected to be quite rigid, but in our computer models and in the actual images, we discovered that the stalks are extremely flexible," said study co-author Gerhard Hummer from the Max Planck Institute of Biophysics.
"Like a balloon on a string, the spikes appear to move on the surface of the virus and thus are able to search for the receptor for docking to the target cell," explained Jacomine Krijnse Locker, another co-author of the study.
While these spikes on the virus' surface are targeted by the immune system's antibodies to prevent infection, the scientists said the entire protein, including the stalk, is covered with chains of glycans.
They said these chains provide a "kind of protective coat" that hides the spikes from the body's neutralising antibodies.
The scientists believe the findings offer valuable insights that can be used for the development of vaccines and therapeutics to treat infected patients.