SD1/SD2 arrangement diversity of the VWF C4 domain. (A) Twist/tilt distribution of VWF C4 domain SD1/SD2 arrangements (wt, left; Y2561 variant, right) estimated by MD simulations. The counts of MD models are shown as a heat map and as histograms along the tilt and twist axes. The heat map colors are defined by counts, as indicated on the right. Highly populated SD1/SD2 arrangements (clusters) are indicated with labels I (wt, Y2561), II (wt, Y2561), and III (Y2561 only). A scheme illustrating the definition of twist and tilt angles is inserted, using colors consistent in panel B. (B) Representative examples of SD1/SD2 arrangement clusters I, II, and III are shown, and their approximate population densities are indicated by “+” signs. Centers of mass used for calculating tilt and twist angles are shown as colored spheres and connected by gray sticks.