The System of Catalysis. Within the superimposed frameworks of IdeS, papain, and cathepsin B, the catalytic cysteine (Cys-94a€“Ser, Cys-25, and Cys-29, correspondingly) and histidine (His-262, His-159, and His-199) residues align perfectly. Hence Cys-94a€“Ser in IdeS is found at N-terminal region of helix I±1 during the software between the L and roentgen domains. To show the higher level of similarity regarding the general geometry of catalytic triad, an extra fitting with respect to the productive website is done (Fig. 2).
The active-site region of IdeS resembles that found in the papain cysteine proteinase superfamily