ACE2 and infection: Moreover, as a first step towards uncovering the mechanism, we could show that Ag NPs but not AgNO3 perturbed the secondary structure of the S-protein which could interfere with proteolytic processing of the S-protein that is required for infection of host cells (Hoffmann et al., 2020a; Hoffmann et al., 2020b), and/or with the binding of cellular receptors such as ACE2.