Figure 1.

Diffraction pattern, electron density and structure of SERCA–Ca₂–AMPPCP. (a) Representative diffraction pattern of SERCA–Ca₂–AMPPCP microcrystals. The boxed inset shows a strong Bragg spot at 2.8 Å resolution {Miller index [31, −15, 24], 〈I/σ(I)〉 = 8.4}. (b) Left, overall 2mF _o − DF _c electron-density map (contoured at 1.0σ) after final refinement including coordinates and B factors for all atoms and data to 2.8 Å resolution; right, molecular model, including ten transmembrane helices and cytoplasmic N (nucleotide binding), P (phosphorylation) and A (actuator) domains. The 13 structural segments initially refined as rigid groups are shown in different colours. Ligand-binding regions are indicated by numbers: 1, AMPPCP; 2, Ca²⁺ ions; 3, lipid.