Explainer: What is a spike protein?

These spikes protrude from the outside of coronaviruses and help them infect cells

An artist’s depiction of a virus particle covered with spike proteins (here colored orange-red). Those spikes bind to cells and help the virus release its genetic material to infect them.

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Members of the coronavirus family have sharp bumps that protrude from the surface of their outer envelopes. Those bumps are known as spike proteins. They’re actually glycoproteins. That means they contain a carbohydrate (such as a sugar molecule). Spiked proteins are what give the viruses their name. Under the microscope, those spikes can appear like a fringe or crown (and corona is Latin for crown).

Spike proteins play an important role in how these viruses infect their hosts.

Examples of coronaviruses include those that cause Severe Acute Respiratory Syndrome (SARS) and Middle East respiratory syndrome (MERS). Their spike proteins work a bit like shape-shifting lock picks. They can change shape to interact with a protein on the surface of human cells. Those spike proteins latch the virus onto a cell. This allows them to get entry into those cells.

On February 19, 2020, researchers described the 3-D structure of the spike protein on the novel coronavirus behind the 2020 global pandemic. This confirmed that the new virus’s spike protein also is a shape-shifter. What’s more, it clings to its target on human cells 10 to 20 times as tightly as the SARS spike protein does to the same target. Such a tight grip may help the COVID-19 virus spread more easily from person to person, researchers now say.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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