Specifically, after the RBD in the S1 subunit of SARS-CoV-2 S protein on the virion binds to the ACE2 receptor on target cells, the FDs in the S2 subunit of the S protein undergo conformational changes and interact with each other, thus bringing the viral and cellular membranes into close proximity and allowing for the fusion peptide be inserted into the host target cell membrane for fusion, thus facilitating viral infection as well as transmission42. This evidence concerns the gene PROS1 and viral infectious disease.