Entrance of coronavirus into cells happens through the spike proteins on the virus surface, for which the spike protein should be cleaved into S1 and S2 domains. This cleavage is mediated by furin, which can specifically cleave Arg-X-X-Arg↓ sites of the substrates. Furin, a member of proprotein convertases family, is moved from the trans-Golgi network to the cell membrane and activates many precursor proteins. A number of pathological conditions such as atherosclerosis, cancer, and viral infectious diseases, are linked with the impaired activity of this enzyme.
Despite the urgent need to control COVID-19, no approved treatment is currently known. Here, folic acid (folate), a water-soluble B vitamin, is introduced for the first time for the inhibition of furin activity. As such, folic acid, as a safe drug, may help to prevent or alleviate the respiratory involvement associated with COVID-19.