Figure 3.

Ca²⁺- and BChl a-binding sites in the Allochromatium tepidum LH1 complex.A, a typical Ca²⁺-binding site in LH1. Color scheme: LH1-α, green; LH1-β, light-blue; Ca²⁺, orange ball. B, a typical BChl a-binding site in an α1/β1 back-to-back subunit showing hydrogen bondings around the BChl a C3-acetyl groups. C, superposition of Cα carbons of the α1-polypeptide with that of α2-polypeptides showing that the C-terminus of the α2-polypeptide disrupts the Ca²⁺-binding site. D, superposition of Cα carbons of the α1-polypeptide with that of α3-polypeptide showing that the C-terminal region of the α3-polypeptide adopts a different conformation from that of the α1-polypeptide around the Ca-binding site. All distances are in ångstrom. BChl, bacteriochlorophyll; LH1, light-harvesting complex.