Figure 5.

Organization of the (bacterio)chlorophyll and carotenoid molecules in LH2 and LHCII. (A) A slice of the nonameric structure of the LH2 complex from Rbl. acidophilus viewed in parallel with the membrane plane and from the outside of the protein. For clarity the central outer helix from three α/β-apoprotein dimers has been removed, allowing the interaction of the carotenoid (orange) with its nearest neighbor, (B)Chl a (green) molecules to be visualized. The contacts between Car and (B)Chl molecules essentially occur at the very end of the C=C conjugated chain of the carotenoid. Protein Data Bank accession number 1KZU. (B) View of a monomer of LHCII from Spinacia oleracea in parallel with the membrane plane. The colors of the two luteins (L), neoxanthin (neo), and xanthophyll (xan) cycle carotenoids are orange, purple, and magenta, respectively. The Chl a and Chl b molecules are colored green and blue, respectively. The closest contacts between Chl a and luteins in LHCII occur at the middle of the C=C polyenic chain. Although the Chl molecules have a pseudosymmetry within the monomer, lutein 1 (L1) and lutein 2 (L2) experience a different protein environment. Protein Data Bank accession number 1RWT.