ACE2 is short for Angiotensin-Converting Enzyme 2, because it “converts” the peptide angiotensin II into angiotensin. Angiotensin II tells your body’s blood vessels to get smaller which raises blood pressure, but angiotensin tells them to get larger and lowers blood pressure. In this way, ACE2’s job is to lower blood pressure.
ACE2 lives in the membranes of cells in human lungs, small intestines, arteries and veins. It stretches from the inside of the cell, through the membrane, to the outside of the cell. The piece of ACE2 that lives outside of the cell is the piece that converts angiotensins, which allows the angiotensin signals to be spread easily from cell to cell.
The viruses SARS-CoV and SARS-CoV-2 recognize good host cells by looking for ACE2. The viruses use their Spike proteins to bind to ACE2, then begin their invasion into the host cell (read about Spike here!). This explains why COVID-19 greatly impacts the respiratory system, since ACE2 is found abundantly in lung cells. Some studies have also shown that patients taking drugs that activate ACE2, intended to lower blood pressure, can be risky for SARS or COVID-19 infections (though many factors influence this risk).
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Chan, K. K., Dorosky, D., Sharma, P., Abbasi, S. A., Dye, J. M., Kranz, D. M., Herbert, A. S., & Procko, E. (2020). Engineering human ACE2 to optimize binding to the spike protein of SARS coronavirus 2. Science (New York, N.Y.), 369(6508), 1261–1265. https://doi.org/10.1126/science.abc0870