Protein dynamics revealed in the excitonic spectra of single LH2 complexes

L. Valkunas, J. Janusonis, D. Rutkauskas, R. van Grondelle

Research output: Contribution to JournalArticleAcademicpeer-review


The fluorescence emission spectrum of single peripheral light-harvesting (LH2) complexes of the photosynthetic purple bacterium Rhodopseudomonas acidophila exhibits remarkable dynamics on a time scale of several minutes. Often the spectral properties are quasi-stable; sometimes large spectral jumps to the blue or to the red are observed. To explain the dynamics, every pigment is proposed to be in two conformational substates with different excitation energies, which originate from the conformational state of the protein as a result of pigment–protein interaction. Due to the excitonic coupling in the ring of 18 pigments, the two-state assumption generates a substantial amount of distinct spectroscopic states, which reflect part of the inhomogeneous distributed spectral properties of LH2. To describe the observed dynamics, spontaneous and light-induced transitions are introduced between the two states. For each ‘realization of the disorder’, the spectral properties are calculated using a disordered exciton model combined with the modified Redfield theory to obtain realistic spectral line shapes. The single-molecule fluorescence peak (FLP) distribution, the distribution dependence on the excitation intensity, and the FLP time traces are well described within the framework of this model.
Original languageEnglish
Pages (from-to)269-275
Number of pages7
JournalJournal of Luminescence
Issue number1
Early online date27 Feb 2007
Publication statusPublished - Nov 2007

Bibliographical note

Part of special issue: Proceedings of the Ninth International Meeting on Hole Burning, Single Molecule, and Related Spectroscopies: Science and Applications. Edited by Jean-Pierre Galaup, Ivan Lorgeré, Jean-Louis LeGouët


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