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Figure 5.
Figure 5. Calcium and cyanocobalamin binding in BtuB a,
Stereo view of the 'aspartate cage' binding the two calcium ions
(yellow) in the Ca^2+ -BtuB and Ca^2+ -B[12] -BtuB structures.
b, Stereo view of cyanocobalamin bound to BtuB. The view is
normal to the surface of the outer membrane, looking down into
the extracellular side. Residues within 4.5 Å of the substrate
are shown, with those of the hatch domain colored purple and
those from the barrel colored green. The calcium ions are
included to indicate the orientation of the molecule (which is
the same as that of Fig. 1).
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