Following interaction, Sp is cleaved by serine proteases, such as transmembrane protease serine 2 (TMPRSS2), into two subunits during infection: the N-terminal S1 fragment containing the RBD bound to ACE2-PD, and the C-terminal S2 fragment responsible for the membrane fusion of the virus with the host cell [13]. Here, TMPRSS2 is linked to infection.