PSMD1 and infection: The process of cell infection occurs in multiple steps: the N-terminal portion of S1 binds to ACE2, and the receptor transmembrane protease serine 2 (TMPRSS2) catalyzes the cleavage between S1 and S2, and finally the viral S2 protein undergoes a conformational rearrangement allowing the fusion between the viral and cellular membrane, and thus the release of viral RNA into the cytoplasm.