Close-up stereo views of the P5-P3′ region of the RCL of PN1 in the active site of thrombin for the 2 complexes. (A) Thrombin is shown in ribbon diagram (gray) in the standard orientation, with the side chains of the catalytic triad shown as sticks and the oxyanion hole represented by blue balls. The RCL of complex 1 is in cyan and that of complex 2 is in yellow, and both are in stick representation from P5 (left) to P3′ (right). In complex 1, the main chain oxygen atom of P1 arginine is not hydrogen bonded to the oxyanion hole. (B) A surface view of thrombin (colored according to electrostatics) illustrates how the RCL of the first complex exits the active site of thrombin at P1′, and how the side chain of Glu192 (indicated) serves to bifurcate the active site into a productive engagement channel (occupied by the RCL of PN1 in complex 2, yellow), and a nonproductive channel (occupied by the RCL of PN1 in complex 1, cyan).