Figure 3. Crystal structure of the Factor IXa protease-EGF2 fragment (1RFN). A ribbon diagram was created with PyMOL. The EGF2 domain is positioned below the protease domain, with the active site oriented upward. The active site S195, and surface residues H92, K126, N129, K132, R165, R170, N178, R233, and R241 are labeled and highlighted with a space filling representation of their respective side chains. The protease heparin-binding exosite is centered near the side chains of R165 and R233.