Researchers in China have found further similarities between 2019-nCoV and SARS. It is now known that 2019-nCoV and SARS both bind to angiotensin-converting enzyme 2 (ACE2) to enter into cells.
ACE2 is a zinc metalloenzyme and carboxypeptidase present on the surface of endothelial (and other) cells. ACE2 acts as a receptor for the severe acute respiratory (SARS) virus. Researchers in China have shown that 2019-nCoV also binds to ACE2 via proteins on the surface of the virus, giving it free passage inside cells.
The researchers at the Wuhan Institute of Virology in China isolated 2019-nCoV from seven patients and successfully infected lab-grown cells that had the ACE2 protein on the surface but failed to infect cells that lacked ACE2. The researchers found that the virus could infect human cells with ACE2, but also cells from bats, civets, and pigs that had ACE2. The researchers said 2019-nCoV closely resembles other coronaviruses that have been found in bats, suggesting bats are most likely the source of the virus.
It is currently unknown how 2019-nCoV is transmitted between patients. It is been established that 2019-nCoV can be transmitted days before patients start showing symptoms of infection, which is part of the reason why the virus has spread so quickly. By the time patients experience symptoms and are confirmed as being infected and are quarantined, they could have passed the virus onto many other people.
Transmission before symptoms makes 2019-nCoV similar to viruses such as influenza. However, influenza is understood to bind to sialic acid on the cell surface to gain entry into cells, not ACE2. Sialic acid is found on cells in the upper respiratory system whereas cells with ACE2 are found deeper in the lungs. The researchers note that in contrast to SARS, 2019-nCoV has additional proteins on its surface which they suggest may allow the virus to bind with sialic acid proteins, although further research is required to determine whether that is the case.
Image Source: CDC/ Alissa Eckert, MS; Dan Higgins, MAM