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Photosynthesis Research

, Volume 123, Issue 1, pp 23–31 | Cite as

The origin of the split B800 absorption peak in the LH2 complexes from Allochromatium vinosum

  • Alexander Löhner
  • Anne-Marie Carey
  • Kirsty Hacking
  • Nichola Picken
  • Sharon Kelly
  • Richard Cogdell
  • Jürgen Köhler
Regular Paper

Abstract

The absorption spectrum of the high-light peripheral light-harvesting (LH) complex from the photosynthetic purple bacterium Allochromatium vinosum features two strong absorptions around 800 and 850 nm. For the LH2 complexes from the species Rhodopseudomonas acidophila and Rhodospirillum molischianum, where high-resolution X-ray structures are available, similar bands have been observed and were assigned to two pigment pools of BChl a molecules that are arranged in two concentric rings (B800 and B850) with nine (acidophila) or eight (molischianum) repeat units, respectively. However, for the high-light peripheral LH complex from Alc. vinosum, the intruiging feature is that the B800 band is split into two components. We have studied this pigment–protein complex by ensemble CD spectroscopy and polarisation-resolved single-molecule spectroscopy. Assuming that the high-light peripheral LH complex in Alc. vinosum is constructed on the same modular principle as described for LH2 from Rps. acidophila and Rsp. molischianum, we used those repeat units as a starting point for simulating the spectra. We find the best agreement between simulation and experiment for a ring-like oligomer of 12 repeat units, where the mutual arrangement of the B800 and B850 rings resembles those from Rsp. molischianum. The splitting of the B800 band can be reproduced if both an excitonic coupling between dimers of B800 molecules and their interaction with the B850 manifold are taken into account. Such dimers predict an interesting apoprotein organisation as discussed below.

Keywords

Light-harvesting complexes Allochromatium vinosum Single-molecule spectroscopy 

Notes

Acknowledgments

A. L. and J. K. thankfully acknowledge financial support by the Deutsche Forschungsgemeinschaft (GRK1640) and the State of Bavaria within the initiative “Solar Technologies go Hybrid”. A.-M. C. is supported as a part of the Photosynthetic Antenna Research Centre (PARC), an Energy Frontier Research Centre funded by the DOE, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC 0001035. She carried out the Car: Bchl ratio study and the CD spectroscopy (with K.H. and S.K.). K. H. is supported by an EPSRC studentship. R. J. C. thanks both DOE and BBSRC for support.

Supplementary material

11120_2014_36_MOESM1_ESM.eps (638 kb)
Supplementary material 1 (EPS 637 kb)

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Copyright information

© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  • Alexander Löhner
    • 1
  • Anne-Marie Carey
    • 2
  • Kirsty Hacking
    • 2
  • Nichola Picken
    • 2
  • Sharon Kelly
    • 2
  • Richard Cogdell
    • 2
  • Jürgen Köhler
    • 1
  1. 1.Experimental Physics IV and Bayreuth Institute for Macromolecular Research (BIMF)University of BayreuthBayreuthGermany
  2. 2.Institute of Molecular, Cell & Systems Biology, College of Medical Veterinary and Life SciencesUniversity of GlasgowGlasgowUK

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