Fig. 1.

A) Fusion of the coronavirus envelop to the (Aa) host cell membrane (Hoffmann et al., 2020), or (Ab) endo-lysosomal membrane (Adedeji et al., 2013); B) Ribbon drawing structure of cathepsin L. Green ribbon: the fold of the two-chain form of native cathepsin L; Blue: α-helices; Red: β-sheets; Ball and stick: the side chains of the reactive-site cysteine (Cys25) and histidine (His163) (Turk et al., 2012); Ribbon drawing structures of C) cystatin and oryzacystatin, D) bromelain inhibitor VI and E) diferric bovine lactoferrin, which show cathepsin L inhibitory activity. Bromelain inhibitor VI and lactoferrin specifically inhibit cathepsin L (no other cathepsins); F) Structural drawings of human cathpesin L suprposed by bovine lactoferrin. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)