title: Structure of the light-harvesting bacteriochlorophyll c assembly in chlorosomes from Chlorobium limicola determined by solid-state NMR.
abstract: We have determined the atomic structure of the bacteriochlorophyll c (BChl c) assembly in a huge light-harvesting organelle, the chlorosome of green photosynthetic bacteria, by solid-state NMR. Previous electron microscopic and spectroscopic studies indicated that chlorosomes have a cylindrical architecture with a diameter of approximately 10 nm consisting of layered BChl molecules. Assembly structures in huge noncrystalline chlorosomes have been proposed based mainly on structure-dependent chemical shifts and a few distances acquired by solid-state NMR, but those studies did not provide a definite structure. Our approach is based on (13)C dipolar spin-diffusion solid-state NMR of uniformly (13)C-labeled chlorosomes under magic-angle spinning. Approximately 90 intermolecular C C distances were obtained by simultaneous assignment of distance correlations and structure optimization preceded by polarization-transfer matrix analysis. It was determined from the approximately 90 intermolecular distances that BChl c molecules form piggyback-dimer-based parallel layers. This finding rules out the well known monomer-based structures. A molecular model of the cylinder in the chlorosome was built by using this structure. It provided insights into the mechanisms of efficient light harvesting and excitation transfer to the reaction centers. This work constitutes an important advance in the structure determination of huge intact systems that cannot be crystallized.
authors.affiliation: Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita 565-0871, Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Egawa
authors.forename: Toshimichi
authors.initials: T
authors.lastname: Fujiwara
authors.forename: Tadashi
authors.initials: T
authors.lastname: Mizoguchi
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kakitani
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Koyama
authors.forename: Hideo
authors.initials: H
authors.lastname: Akutsu
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001429:Bacteriochlorophylls / Q000737:chemistry* / Q000378:metabolism*; D041883:Chlorobium / Q000737:chemistry* / Q000378:metabolism* / Q000528:radiation effects; D004058:Diffusion; D019281:Dimerization; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; C002084:bacteriochlorophyll c