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

Löhner, A., Carey, A.-M., Hacking, K., Picken, N., Kelly, S. , Cogdell, R. and Köhler, J. (2015) The origin of the split B800 absorption peak in the LH2 complexes from Allochromatium vinosum. Photosynthesis Research, 123(1), pp. 23-31. (doi:10.1007/s11120-014-0036-2)

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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.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Picken, Dr Nichola and Cogdell, Professor Richard and Kelly, Dr Sharon and Hacking, Dr Kirsty
Authors: Löhner, A., Carey, A.-M., Hacking, K., Picken, N., Kelly, S., Cogdell, R., and Köhler, J.
College/School:College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
Journal Name:Photosynthesis Research
Publisher:Springer
ISSN:0166-8595
ISSN (Online):1573-5079
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
502612Photosynthetic Antenna Research Center (PARC)Richard CogdellUS Department of Energy (DEN)DE-SC0001035RI MOLECULAR CELL & SYSTEMS BIOLOGY