In Vitro Characterization of Inhibition Function of Calcifediol to the Protease Activity of SARS-COV-2 PLpro

Vitamin D3 and its metabolites calcifediol have been recommended as effective drugs for novel coronavirus disease 2019 (COVID-19) therapy in many studies, since the outbreak of this global dramatic pandemic. In this study, we made a striking discovery that Calcifediol demonstrates robust inhibitive effect on the of the papain-like cysteine protease (PLpro), a critical proteolytic enzyme for the severe acute respiratory syndrome coronavirus-2(SARS-COV-2), through a small-scale FRET-based screening experiment. The practical bindings of Calcifediol to PLpro were also demonstrated by several in vitro interaction studies. All the evidence had revealed the inhibition might be caused by the targeted binding event. Consequently, our discovery represents a significant finding that the beneficial therapeutic impact of Calcifediol on COVID-19 may be attributed not only to its immunoregulatory properties but also to its inhibition of PLpro. This finding strongly bolsters the case for the clinical use of Vitamin D3 and its derivative Calcifediol in the treatment of COVID-19.