title: Single-molecule spectroscopy reveals that individual low-light LH2 complexes from Rhodopseudomonas palustris 2.1.6. have a heterogeneous polypeptide composition.
abstract: Rhodopseudomonas palustris belongs to the group of purple bacteria that have the ability to produce LH2 complexes with unusual absorption spectra when they are grown at low-light intensity. This ability is often related to the presence of multiple genes encoding the antenna apoproteins. Here we report, for the first time to our knowledge, direct evidence that individual low-light LH2 complexes have a heterogeneous alphabeta-apoprotein composition that modulates the site energies of Bchl a molecules, producing absorption bands at 800, 820, and 850 nm. The arrangement of the Bchl a molecules in the "tightly coupled ring" can be modeled by nine alphabeta-Bchls dimers, such that the Bchls bound to six alphabeta-pairs have B820-like site energies and the remaining Bchl a molecules have B850-like site energies. Furthermore, the experimental data can only be satisfactorily modeled when these six alphabeta-pairs with B820 Bchl a molecules are distributed such that the symmetry of the assembly is reduced to C(3). It is also clear from the measured single-molecule spectra that the energies of the electronically excited states in the mixed B820/850 ring are mainly influenced by diagonal disorder.
authors.affiliation: Division of Molecular and Cellular Biology, Faculty of Biomedical and Life Sciences, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Tatas H P
authors.initials: TH
authors.lastname: Brotosudarmo
authors.forename: Ralf
authors.initials: R
authors.lastname: Kunz
authors.forename: Paul
authors.initials: P
authors.lastname: Böhm
authors.forename: Alastair T
authors.initials: AT
authors.lastname: Gardiner
authors.forename: Vladimíra
authors.initials: V
authors.lastname: Moulisová
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Cogdell
authors.forename: Jürgen
authors.initials: J
authors.lastname: Köhler
mesh_terms: D000042:Absorption; D001426:Bacterial Proteins / Q000737:chemistry*; D003198:Computer Simulation; D005453:Fluorescence; D005454:Fluorescence Polarization; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008029:Lighting; D008956:Models, Chemical; D012241:Rhodopseudomonas / Q000737:chemistry*; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: C081521:B800-850 light-harvesting complex, bacteria; D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes