title: Spectral heterogeneity and carotenoid-to-bacteriochlorophyll energy transfer in LH2 light-harvesting complexes from Allochromatium vinosum.
abstract: Photosynthetic organisms produce a vast array of spectral forms of antenna pigment-protein complexes to harvest solar energy and also to adapt to growth under the variable environmental conditions of light intensity, temperature, and nutrient availability. This behavior is exemplified by Allochromatium (Alc.) vinosum, a photosynthetic purple sulfur bacterium that produces different types of LH2 light-harvesting complexes in response to variations in growth conditions. In the present work, three different spectral forms of LH2 from Alc. vinosum, B800-820, B800-840, and B800-850, were isolated, purified, and examined using steady-state absorption and fluorescence spectroscopy, and ultrafast time-resolved absorption spectroscopy. The pigment composition of the LH2 complexes was analyzed by high-performance liquid chromatography, and all were found to contain five carotenoids: lycopene, anhydrorhodovibrin, spirilloxanthin, rhodopin, and rhodovibrin. Spectral reconstructions of the absorption and fluorescence excitation spectra based on the pigment composition revealed significantly more spectral heterogeneity in these systems compared to LH2 complexes isolated from other species of purple bacteria. The data also revealed the individual carotenoid-to-bacteriochlorophyll energy transfer efficiencies which were correlated with the kinetic data from the ultrafast transient absorption spectroscopic experiments. This series of LH2 complexes allows a systematic exploration of the factors that determine the spectral properties of the bound pigments and control the rate and efficiency of carotenoid-to-bacteriochlorophyll energy transfer.
authors.affiliation: Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, CT, 06269-3060, USA.
authors.forename: Nikki M
authors.initials: NM
authors.lastname: Magdaong
authors.affiliation: Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, CT, 06269-3060, USA.
authors.forename: Amy M
authors.initials: AM
authors.lastname: LaFountain
authors.affiliation: Institute of Molecular Cell and Systems Biology, University of Glasgow, Glasgow, Scotland, UK.
authors.forename: Kirsty
authors.initials: K
authors.lastname: Hacking
authors.affiliation: Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO, USA.
authors.forename: Dariusz M
authors.initials: DM
authors.lastname: Niedzwiedzki
authors.affiliation: Department of Physics, University of Connecticut, 2152 Hillside Road, Storrs, CT, 06269-3046, USA.
authors.forename: George N
authors.initials: GN
authors.lastname: Gibson
authors.affiliation: Institute of Molecular Cell and Systems Biology, University of Glasgow, Glasgow, Scotland, UK.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Cogdell
authors.affiliation: Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, CT, 06269-3060, USA. harry.frank@uconn.edu.
authors.forename: Harry A
authors.initials: HA
authors.lastname: Frank
mesh_terms: D001429:Bacteriochlorophylls / Q000378:metabolism*; D002338:Carotenoids / Q000378:metabolism*; D002841:Chromatiaceae / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004735:Energy Transfer; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D002338:Carotenoids
keywords: Carotenoids; Energy transfer; Light-harvesting; Photosynthesis; Pigment-protein complex; Ultrafast transient absorption spectroscopy