In either case, proteases are required for viral infection, such as angiotensin-converting enzyme 2 (ACE2), which interacts with viral protein S, as well as furin cleavage and superficial serine two transmembrane protease (TMPRSS2), which are key to membrane fusion and L-cathepsin by endocytosis [273,274]. This evidence concerns the gene ACE2 and viral infectious disease.