Model of full-length membrane-docked pseutarin C. (A) A model of the full-length pseutarin C complex (fXa in cyan and fVa colored as in Fig. 1), including missing loops and domains (the a1 loop in magenta), is shown bound to a phospholipid membrane surface (a lipid bilayer is shown as sticks). The Gla domain of fXa (calcium ions depicted as green spheres) and the membrane-binding C domains of fVa are coplanar, suggesting a similar extent of membrane penetration. A ∼10-Å penetration into the membrane is consistent with previous fluorescence resonance energy transfer measurements from the membrane to residue Cys540 of the A2 domain and to the active site of fXa in human prothrombinase (measurements indicated in right panel; EGRCK inhibitor shown as spheres). (B) The nature of the fVa-fXa interface is illustrated by coloring the surface of fVa according to electrostatic potential (red, negative; blue, positive) and showing fXa as a semitransparent cartoon. (C) The surface of fXa is shown colored according to electrostatics (highly basic region indicated by oval), with fVa (semitransparent, colored as in panel A).