Furin and its role in CoronaVirus cellular Entry
The corona virus contains what is called a spike protein, which is essential for binding and entry into our cells. We can think of this spike protein, as being the sticky part of the virus, much like sticker plants that stick to our pant legs.
In the case of corona virus, the spike protein sticks to our cells, and then is able to gain entry. We can also think of the spike protein like a key, that is able to open a lock (ACE-2 receptors) on the surface of our cells. When the key opens the lock the virus can enter. In order for the spike protein to become active and act like a key, which is able to open the ACE-2 receptor (lock), the key (spike protein) must first be cleaved (cut) so that it can become active. [1, 2]
A protein that exists in our body, called furin, is what activates the spike protein, and allows it to open up the cell to gain entry. Furin is also known to activate other pathogens such as HIV, influenza, dengue, filoviruses, ebola and marburg virus. Additionally, Anthrax toxin, pseudomonas exotoxin, and papillomaviruses are also activated by furin. 
One possible way to stop the coronavirus from entering our cells is to inhibit the protein furin. By preventing furin from activating the spike protein, it may be able to stop the coronavirus from entering our cells.
Research on Dengue virus has shown that a naturally occurring substance called luteolin, is able to inhibit furin and therefore restrict viral replication.
As the coronavirus gains entry into our cells, in part due to furin, it may be beneficial to consume foods and herbs that are high in luteolin. Since the luteolin inhibits the activity of furin, this is one possible way to prevent the virus from gaining entry into our cells.
What is Luteolin?
Luteolin is a naturally occurring compound found in many plants, foods, and herbs. According to the U.S. National Library of Medicine and National Institute of Health website, luteolin and has anti-cancer, anti-inflammatory, and anti-oxidant properties.  National Institute of Health, Luteolin
Read the next article called Foods High in Luteolin.
1. Furin cleavage site in the SARS-CoV-2 coronavirus glycoprotein
Racaniello, Virology Blog
Antiviral Res. 2017 Jul;143:176-185. doi: 10.1016/j.antiviral.2017.03.026. Epub 2017 Apr 5.
Peng, Watanabe, Chan, He, Zhao, Zhang, Lai,, Luo, Vasudevan, Li.
3. Wikipedia, Furin
4. National Institue of Health, U.S. National Library of Medicine, National Center for Biotechnology Information https://pubchem.ncbi.nlm.nih.gov/compound/luteolin