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Figure 4.
Figure 4: Details of the transmembrane Ca^2+-binding sites.
The refined model is superimposed with a 2|F[o]| - |F[c]|
composite-omit map prepared with CNS (blue meshes, contoured at
1.5  ).
The meshes in pink show omit |F[ o]| - |F[c]| map for Ca^2+ and
a bound water (cut-off at 3 ).
Blue spheres represent Ca^ 2+, and red spheres water molecules.
Viewed roughly normal to the membrane from the cytoplasmic side
(a) and parallel to the membrane (b) in stereo. The
coordinations of oxygen atoms to Ca^2+ are indicated by white
dotted lines, and possible hydrogen bonds stabilizing the
coordination geometry by green dashed lines. The viewing
direction in b is also specified in Fig. 3a. Water molecule
nearest to the Ca^ 2+-binding site is marked (asterisk). Note
the unwinding of helices M4 and M6 and rows of exposed carbonyl
oxygen atoms along these helices in b.
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