Structure of human cathepsin B inhibited with ca030. Cathepsin B belongs to the same family as papain, and therefore its fold is representative of the papain-like fold. In this fold, the active site cleft is surrounded by two domains. The N-terminal domain is rich in alpha helices, whereas the C-terminal domain contains a beta barrel.
The catalitic site is a catalytic triad with a charge relay system*. This triad includes Cys115, His272, and Asn296.
*See family C26 for a more detailed explanation of the charge relay system in a catalytic triad.



  • Structures are rendered as ribbons. Catalytic and catalytic metal-complexing residues are shown as neons. Inhibitors are displayed as space filling spheres.

  • Carbons are shown in light gray, hydrogens in cyan, oxygens in red, nitrogens in blue, and sulfurs in yellow.

  • Left-click and drag to rotate the protease. Right-click and drag up/down to zoom in/out. Click with both buttons and drag to move the protease. Use the upper bar to get different views and for display options. For a close-up of the catalytic site, choose the cat_site view.

  • Once you have clicked inside the structure window, you can use the keyboard to hide/show objects:

    '1' toggles the ribbon.
    '2' toggles the inhibitor.
    '3' toggles the catalytic residues.

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  • To hide/show elements in the structure, first you have to click inside the render window.