Cellular recognition and binding to ACE2’s PD via the RBD is proposed to initiate a series of complex conformational transitions in the S homotrimeric protein, leading to the shedding of its S1 subunit and fusion to the host cell membrane driven by the S2 subunit (22, 23, 24, 25, 26), ultimately resulting in the infection of the host cell. Here, ACE2 is linked to infection.