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

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...

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Bibliographic Details
Published in:Photosynthesis research 2015-01, Vol.123 (1), p.23-31
Main Authors: Löhner, Alexander, Carey, Anne-Marie, Hacking, Kirsty, Picken, Nichola, Kelly, Sharon, Cogdell, Richard, Köhler, Jürgen
Format: Article
Language:English
Subjects:
absorption
Allochromatium vinosum
bacteria
Biochemistry
Biomedical and Life Sciences
Circular Dichroism
circular dichroism spectroscopy
Gammaproteobacteria - physiology
Life Sciences
Light-Harvesting Protein Complexes - physiology
luteinizing hormone
Models, Biological
Monte Carlo Method
Phaeospirillum molischianum
Photosynthesis
Pigments
Pigments, Biological - physiology
Plant Genetics and Genomics
Plant Physiology
Plant Sciences
Protein Conformation
Proteins
Regular Paper
Rhodopseudomonas acidophila
Rhodospirillum molischianum
Spectrophotometry, Atomic
Spectrum analysis
X-radiation
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Summary: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.
ISSN:0166-8595
1573-5079
DOI:10.1007/s11120-014-0036-2