MARK2 and COVID-19: As a negative control for the serine/threonine kinase GLK, ACE2 Tyr781 phosphorylation was not detected in ACE2 proteins from GLK in vitro kinase assay (Fig 5C), albeit it was detected in the ACE2 peptide from the serum samples of COVID‐19 patients in Cohort #4 (Appendix Fig S7B).