ACE2 and COVID-19: Unexpectedly, we identified a non-RBD-blocking monoclonal antibody (mAb, clone 3H3, derived from convalescent COVID-19 patients), which was reported to bind both S1 and S2 subdomains of the spike protein and have high neutralization activity against SARS2 infection through ACE2 with no clear mechanisms.50 Single-molecule MT pulling experiments showed that this antibody significantly impedes S1/S2 detachment.