ACE2 and COVID-19: Of these, the spike protein is particularly critical because it mediates viral binding to SARS-CoV-2 receptors [angiotensin converting enzyme-2 (ACE2) (1, 4–7), neuropilin-1 (6, 7), and heparan sulfate (8, 9)], catalyzes the fusion of viral and cellular membranes (10, 11), is the sole antigen expressed by most SARS-CoV-2 vaccines (12), and is the primary target of antibody-based COVID-19 therapeutics (13, 14).