FIGURE 9.

Diagram of the SERCA Ca²⁺ binding sites in the E1·2Ca²⁺ and in the E2 state stabilized by thapsigargin (TG) and dibutyldihydroxybenzene (BHQ) (44) based on crystallography (12, 42) and continuum of electrostatic calculations. The larger cyan spheres in the upper diagram represent bound Ca²⁺ (I and II), and the small red spheres represent water. Small red circles represent bound protons, dotted pink lines represent hydrogen bonds, and green dotted lines represent Ca²⁺ coordination. The arrows indicate possible movements upon state transition. Data are derived from Obara et al. (44).