Contact regions for PN1 and thrombin in complexes 1 and 2. (A) Ribbon diagram of the top of PN1 of complex 1 is colored cyan to illustrate regions in contact with thrombin (residues with atoms within 5 Å). The principal contacts are the RCL, with only 3 residues comprising the exosite. (B) Surface representation of thrombin (gray, with contact residues in orange) illustrates the extent of interaction with PN1 in complex 1. Contacting PN1 residues are shown as sticks and colored cyan. (C) PN1 from complex 2 is shown in the same orientation as in panel A, colored orange to indicate the extensive interface with thrombin. (D) Surface of thrombin interacting with PN1 in complex 2 is shown, colored as in panel B, but with PN1 residues shown as yellow sticks.