fig1

Figure 1. Complex formation between CatK and C4-S. Electrostatic surface distribution of human CatK. Blue and red areas represent positively and negatively charged surface domains of CatK, respectively (generated using Chimera software). The locations of two C4-S-binding sites (exosites) (PDB accession codes 3C9E and 4N8W) are marked by dashed circles, away from the active site. The pan-inhibitor of cysteine proteases, E-64, is located in the active site of the enzyme. The peptidase is shown in surface representation, while C4-S and E-64 are shown as sticks. CatK: Cathepsin K; C4-S: chondroitin 4-sulfate; PDB: protein data bank.