Schematic 3-D models of human thrombin.

<p>Panel A shows a schematic 3D structure of human thrombin with the charge density illustrated with blue for basic or positively charged regions and red for negatively charged or acidic regions. The color intensity reflects the charge intensity. Panel B shows a schematic 3D structure of human thrombin where some of the positively charged amino acid positions studied by site directed mutagenesis in exosites I and II are marked in blue. The active site serine is shown in green and the histidine and aspartic acids are hidden under an extending loop and therefore not visible in this angle of the molecule. Two extended surface loops, the 60 loop and the γ-loop are shown in yellow and orange, respectively. Thrombin structure from PDB, code 1DM4 run using UCSF Chimera v1.8 and annotated in Adobe Illustrator CS5.