Summary: " …The membrane of coronaviruses harbors a trimeric transmembrane spike (S) glycoprotein which is essential for entry of virus particles into the cell.
The S protein contains two functional domains: a receptor binding domain, and a second domain which contains sequences that mediate fusion of the viral and cell membranes.
The S glycoprotein must be cleaved by cell proteases to enable exposure of the fusion sequences and hence is needed for cell entry.
The spike glycoprotein of the newly emerged SARS-CoV-2 contains a potential cleavage site for furin proteases.
Proteolytic cleavage of the S glycoprotein can determine whether the virus can cross species, e.g. from bats to humans.
Acquisition of the furin cleavage site might be viewed as a ‘gain of function’ that enabled a bat CoV to jump into humans and begin its current epidemic spread.
"
