title: Conformational relaxation of single bacterial light-harvesting complexes.
abstract: We have employed the technique of single-molecule fluorescence microspectroscopy to investigate the spontaneous conformational evolution of individual peripheral LH2 complexes from the purple bacterium Rhodopseudomonas acidophila. Fluorescence microscopy is a sensitive tool, which allows the spectral changes of single complexes to be monitored on a time scale from 0.1 s to many minutes. Here we have investigated "natural" (occurring in the absence of excitation) spectral diffusion after a spectral jump has occurred. In a quarter of all the observed spectral jumps recorded with the LH2 complexes, a further spontaneous evolution occurs, in the absence of illumination, that results in the formation of a different spectroscopic state. We suggest that this is due to a natural conformational development of the pigment-protein complex, which so far has not been observed for this type of complex at the single-molecule level. The functional significance of such structural rearrangements is not yet clear but may be associated with the necessity for the light-harvesting complexes to adjust their shape in the densely packed photosynthetic membrane.
authors.affiliation: Department of Biophysics and Physics of Complex Systems, Division of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands. danielis@nat.vu.nl
authors.forename: Danielis
authors.initials: D
authors.lastname: Rutkauskas
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Cogdell
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D018613:Microscopy, Confocal; D017711:Nonlinear Dynamics; D011487:Protein Conformation; D012241:Rhodopseudomonas / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes