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Biophys J. 2015 Jun 2;108(11):2713-20. doi: 10.1016/j.bpj.2015.04.017.

Conformational switching in a light-harvesting protein as followed by single-molecule spectroscopy.

Author information

1
CEA, Institute of Biology and Technology of Saclay, Gif-sur-Yvette, France; Institute for Integrative Biology of the Cell, Université Paris Saclay, CEA, CNRS, Université Paris Sud, CEA-Saclay, Gif sur Yvette, France. Electronic address: andrew.gall@cea.fr.
2
CEA, Institute of Biology and Technology of Saclay, Gif-sur-Yvette, France; Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands; Institute for Integrative Biology of the Cell, Université Paris Saclay, CEA, CNRS, Université Paris Sud, CEA-Saclay, Gif sur Yvette, France.
3
Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands; Department of Physics, University of Pretoria, Pretoria, South Africa.
4
Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands; A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia.
5
Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands. Electronic address: r.van.grondelle@vu.nl.

Abstract

Among the ultimate goals of protein physics, the complete, experimental description of the energy paths leading to protein conformational changes remains a challenge. Single protein fluorescence spectroscopy constitutes an approach of choice for addressing protein dynamics, and, among naturally fluorescing proteins, light-harvesting (LH) proteins from purple bacteria constitute an ideal object for such a study. LHs bind bacteriochlorophyll a molecules, which confer on them a high intrinsic fluorescence yield. Moreover, the electronic properties of these pigment-proteins result from the strong excitonic coupling between their bound bacteriochlorophyll a molecules in combination with the large energetic disorder due to slow fluctuations in their structure. As a result, the position and probability of their fluorescence transition delicately depends on the precise realization of the disorder of the set of bound pigments, which is governed by the LH protein dynamics. Analysis of these parameters using time-resolved single-molecule fluorescence spectroscopy thus yields direct access to the protein dynamics. Applying this technique to the LH2 protein from Rhodovulum (Rdv.) sulfidophilum, the structure-and consequently the fluorescence properties-of which depends on pH, allowed us to follow a single protein, pH-induced, reversible, conformational transition. Hence, for the first time, to our knowledge, a protein transition can be visualized through changes in the electronic structure of the intrinsic cofactors, at a level of a single LH protein, which opens a new, to our knowledge, route for understanding the changes in energy landscape that underlie protein function and adaptation to the needs of living organisms.

PMID:
26039172
PMCID:
PMC4457476
DOI:
10.1016/j.bpj.2015.04.017
[Indexed for MEDLINE]
Free PMC Article

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