I found some further information outside
of the study with eight participants that
suggest ace-2 is involved.

"If we think of the human body as a house and 2019-nCoV [another name for SARS-CoV-2] as a robber, then ACE2 would be the doorknob of the house's door. Once the S-protein grabs it, the virus can enter the house," Liang Tao, a researcher at Westlake University who was not involved in the new study, said in a statement."

Scientists figure out how new coronavirus breaks into human cells
https://www.livescience.com/how-coronavirus-infects-cells.html

Researchers at Westlake University Unveiled Structure of the RBD-ACE2-B0AT1 Complex
https://en.westlake.edu.cn/news_events/westlakenews/202002/t20200225_3069.shtml

"Structural basis for the recognition of the SARS-CoV-2 by full-length human ACE2"
https://science.sciencemag.org/content/early/2020/03/03/science.abb2762

Apparently, ibuprofen might increase ACE-2, so there is some chatter about that being a bad idea.
https://www.thelancet.com/action/showPdf?pii=S2213-2600%2820%2930116-8