title: Stark absorption spectroscopy on the carotenoids bound to B800-820 and B800-850 type LH2 complexes from a purple photosynthetic bacterium, Phaeospirillum molischianum strain DSM120.
abstract: Stark absorption spectroscopy was applied to clarify the structural differences between carotenoids bound to the B800-820 and B800-850 LH2 complexes from a purple photosynthetic bacterium Phaeospirillum (Phs.) molischianum DSM120. The former complex is produced when the bacteria are grown under stressed conditions of low temperature and dim light. These two LH2 complexes bind carotenoids with similar composition, 10% lycopene and 80% rhodopin, each with the same number of conjugated CC double bonds (n=11). Quantitative classical and semi-quantum chemical analyses of Stark absorption spectra recorded in the carotenoid absorption region reveal that the absolute values of the difference dipole moments |Δμ| have substantial differences (2 [D/f]) for carotenoids bound to either B800-820 or B800-850 complexes. The origin of this striking difference in the |Δμ| values was analyzed using the X-ray crystal structure of the B800-850 LH2 complex from Phs. molischianum DSM119. Semi-empirical molecular orbital calculations predict structural deformations of the major carotenoid, rhodopin, bound within the B800-820 complex. We propose that simultaneous rotations around neighboring CC and CC bonds account for the differences in the 2 [D/f] of the |Δμ| value. The plausible position of the rotation is postulated to be located around C21-C24 bonds of rhodopin.
authors.affiliation: Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Horibe
authors.affiliation: Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield S10 2TN, United Kingdom.
authors.forename: Pu
authors.initials: P
authors.lastname: Qian
authors.affiliation: Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield S10 2TN, United Kingdom.
authors.forename: C Neil
authors.initials: CN
authors.lastname: Hunter
authors.affiliation: Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan; The Osaka City University Advanced Research Institute for Natural Science and Technology (OCARINA), 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan. Electronic address: hassy@ocarina.osaka-cu.ac.jp.
authors.forename: Hideki
authors.initials: H
authors.lastname: Hashimoto
mesh_terms: D065966:Absorption, Physicochemical; D000595:Amino Acid Sequence; D002338:Carotenoids / Q000737:chemistry* / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D010788:Photosynthesis; D012244:Rhodospirillaceae / Q000378:metabolism*; D013057:Spectrum Analysis
chemical_list: D045342:Light-Harvesting Protein Complexes; D002338:Carotenoids
keywords: B800–820 LH2 complex; B800–850 LH2 complex; Carotenoids; Purple photosynthetic bacteria; Stark absorption spectroscopy