title: Probing the electronic structure and conformational flexibility of individual light-harvesting 3 complexes by optical single-molecule spectroscopy.
abstract: We present fluorescence-excitation spectra of individual light-harvesting 3 (LH3 or B800-820) complexes of Rhodopseudomonas acidophila at 1.2 K. The optical single-molecule studies were employed to investigate the electronic structure as well as the conformational flexibility of the individual pigment-protein complexes. The optical spectra resemble those of individual light-harvesting 2 (LH2) complexes, in agreement with the structural similarity of both types of complexes. Although variations among the LH3 spectra are large, there is a distinct difference in the spectral features of the 800 and 820 nm region that appears in all the complexes studied. In the B800 region 4-6 narrow bands are present whereas in the B820 region a limited number of relatively broad bands are observed. These observations can generally be interpreted in terms of localized excitations in the 800 nm region and delocalized excitations in the 820 nm region. The observed heterogeneous spectral behavior, especially in the B820 band, indicates that the B820 pigments of LH3 are sensitive to light-induced local conformational changes. It is suggested that a rotation of the C(3)-acetyl chain of a BChl a pigment bound to the beta-subunit of the light-harvesting complex is the origin of the conformational flexibility and affects the optical properties of the whole pigment-protein complex.
authors.affiliation: Department of Biophysics, Leiden University, 2300 RA Leiden, The Netherlands.
authors.forename: Martijn
authors.initials: M
authors.lastname: Ketelaars
authors.forename: Jean-Manuel
authors.initials: JM
authors.lastname: Segura
authors.forename: Silke
authors.initials: S
authors.lastname: Oellerich
authors.forename: Ward P F
authors.initials: WP
authors.lastname: de Ruijter
authors.forename: Gerhard
authors.initials: G
authors.lastname: Magis
authors.forename: Thijs J
authors.initials: TJ
authors.lastname: Aartsma
authors.forename: Michio
authors.initials: M
authors.lastname: Matsushita
authors.forename: Jan
authors.initials: J
authors.lastname: Schmidt
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Cogdell
authors.forename: Jürgen
authors.initials: J
authors.lastname: Köhler
mesh_terms: D001703:Biophysics / Q000379:methods; D002627:Chemistry, Physical / Q000379:methods; D003198:Computer Simulation; D004563:Electrochemistry / Q000379:methods*; D004581:Electronics; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D015233:Models, Statistical; D008962:Models, Theoretical; D008968:Molecular Conformation; D012241:Rhodopseudomonas / Q000378:metabolism; D013696:Temperature
chemical_list: D045342:Light-Harvesting Protein Complexes