Figure 6.

B800 BChls. (A) The ring of B800 molecules, with Mg–Mg distances of 20.8 Å (Figure 5D), viewed from the cytoplasmic side of the complex. (B) View of the B800 binding site from the exterior of the complex in the plane of the membrane. The polypeptides are in surface representation with the cytoplasmic side uppermost, showing the outer edge of the B800 BChls (cyan), part of the B850 macrocycle and the phytyl tail (green). (C) Fits of a B800 (cyan), carboxymethyl methionine (α-Met1) (yellow), β-His22 (blue), and a water molecule (red sphere) modeled within the density in this region of the complex. (D) Structural model of the B800 binding site showing distances of hydrogen bonds and the coordination with the Mg of B800. β-His22 sits above B800, and β-Arg30 is on the right forming hydrogen bonds with the B800 BChl. The bonding network includes α-Asn3. Two carotenoids are shown, one of which passes close to the B800.