Breathless: The Scientific Race to Defeat a Deadly Virus

by David Quammen

The segment of interest was the gene responsible for producing the spike proteins, the complex knobs on the surface of each spherical virion, which form a corona-like fuzz and give the family its name. The spikes protrude from the envelope (exterior wrapper) of the virion. Each spike consists of three copies of an identical protein bundled together like an inverted tripod. It’s an elaborate, three-dimensional molecular feature that allows a virion to catch hold of a receptor molecule on the exterior of a cell, fuse its envelope with the cell membrane, and gain entry for its RNA genome. You often hear the simile—it’s a go-to cliché—that the spike fits to the receptor like a key to a lock, opening the cell. That’s too simple, because the spike is so intricate and dynamic, but it does capture the fact that precise matching between a spike and a cell receptor is what determines which coronaviruses can infect which cells within which particular host. Matching of spike and receptor also, therefore, affects the capacity for host switching.