Spike is a membrane protein found on the surface of coronaviruses (including SARS-CoV-2, the virus that causes COVID-19). Spike is responsible for bringing the virus inside of the host cell. Both the virus and the host cell are covered in a membrane, and Spike fuses the two membranes together so that viral contents can enter the host cell.
Spike is made of 1281 amino acids (protein building blocks) that form three important functional pieces.
One piece, called the transmembrane region, anchors Spike into the membrane of the virus. The other two pieces stick out from the virus’s membrane; one recognizes proteins on the host cell (these are called ACE2 receptors–read about them here!) and the other works to fuse the viral membrane and the host cell membrane together. The outer pieces of Spike also have sugars attached to them, which help hide the Spike protein from the host’s immune system.
Since Spike lives on the outside of viruses, it is a common target for our immune systems. If our immune systems make antibodies that can recognize the Spike protein, they can attack the virus (learn about antibodies here!). These are the kinds of antibodies that can be detected by COVID-19 antibody tests. We can make antibodies against Spike without ever becoming sick with COVID-19 if we are vaccinated because the vaccines expose us to pieces of Spike.
For the same reason our own bodies target Spike to take out coronaviruses, scientists and pharmacologists are making drugs that target Spike. If we can block Spike’s ability to fuse the viral and host cell membranes, we can prevent infections.
For further investigation:
Saxena A. (2020). Drug targets for COVID-19 therapeutics: Ongoing global efforts. Journal of biosciences, 45(1), 87. https://doi.org/10.1007/s12038-020-00067-w