This Article Full Text Full Text (PDF) supplemental file All Versions of this Article: biophysj.104.047498v1 87/5/3010    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Georgakopoulou, S. Articles by van der Zwan, G. Search for Related Content PubMed PubMed Citation Articles by Georgakopoulou, S. Articles by van der Zwan, G.

Circular Dichroism of Carotenoids in Bacterial Light-Harvesting Complexes: Experiments and Modeling

S. Georgakopoulou ^*, R. van Grondelle ^* and G. van der Zwan 

^* Department of Biophysics and Physics of Complex Systems, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands; and Department of Analytical Chemistry and Applied Spectroscopy, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands

Correspondence: Address reprint requests to Dr. Gert van der Zwan, Vrije Universiteit, Chemistry, de Boelelaan 1883, 1081 HV Amsterdam, The Netherlands. Tel.: 031-020-444-76-35; E-mail: zwan{at}few.vu.nl.

In this work we investigate the origin and characteristics of the circular dichroism (CD) spectrum of rhodopin glucoside and lycopene in the light-harvesting 2 complex of Rhodopseudomonas acidophila and Rhodospirillum molischianum, respectively. We successfully model their absorption and CD spectra based on the high-resolution structures. We assume that these spectra originate from seven interacting transition dipole moments: the first corresponds to the 0-0 transition of the carotenoid, whereas the remaining six represent higher vibronic components of the S₂ state. From the absorption spectra we get an estimate of the Franck-Condon factors of these transitions. Furthermore, we investigate the broadening mechanisms that lead to the final shape of the spectra and get an insight into the interaction energy between carotenoids. Finally, we examine the consequences of rotations of the carotenoid transition dipole moment and of deformations in the light-harvesting 2 complex rings. Comparison of the modeled carotenoid spectra with modeled spectra of the bacteriochlorophyll Q_Y region leads to a refinement of the modeling procedure and an improvement of all calculated results. We therefore propose that the combined carotenoid and bacteriochlorophyll CD can be used as an accurate reflection of the overall structure of the light-harvesting complexes.