Structure of human t-plasminogen activator in complex with an inhibitor. The overall fold of this enzyme corresponds to the trypsin-like clan, also called PA clan. This fold displays two similar beta barrel-containing subdomains with the catalytic site between the barrels. Notably, this fold is not exclusive of serine-proteases, but is also present in certain viral cysteine-proteases.
The catalytic site consists of a triad of residues in a charge relay system*, from Asp406 to His357 to Ser513.
*See family S10 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.

  • You can download the pdf file here

  • To display and manipulate the structure, you need at least Adobe Acrobat Reader v7.0. For best results, install the last version of Acrobat Reader.

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