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Proceedings Paper

Single-molecule exploration of photoprotective mechanisms in light-harvesting complexes
Author(s): Hsiang-Yu Yang; Gabriela S. Schlau-Cohen; Michal Gwizdala; Tjaart Krüger; Pengqi Xu; Roberta Croce; Rienk van Grondelle; W. E. Moerner
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Paper Abstract

Plants harvest sunlight by converting light energy to electron flow through the primary events in photosynthesis. One important question is how the light harvesting machinery adapts to fluctuating sunlight intensity. As a result of various regulatory processes, efficient light harvesting and photoprotection are balanced. Some of the biological steps in the photoprotective processes have been extensively studied and physiological regulatory factors have been identified. For example, the effect of lumen pH in changing carotenoid composition has been explored. However, the importance of photophysical dynamics in the initial light-harvesting steps and its relation to photoprotection remain poorly understood. Conformational and excited-state dynamics of multi-chromophore pigment-protein complexes are often difficult to study and limited information can be extracted from ensemble-averaged measurements. To address the problem, we use the Anti-Brownian ELectrokinetic (ABEL) trap to investigate the fluorescence from individual copies of light-harvesting complex II (LHCII), the primary antenna protein in higher plants, in a solution-phase environment. Perturbative surface immobilization or encapsulation schemes are avoided, and therefore the intrinsic dynamics and heterogeneity in the fluorescence of individual proteins are revealed. We perform simultaneous measurements of fluorescence intensity (brightness), excited-state lifetime, and emission spectrum of single trapped proteins. By analyzing the correlated changes between these observables, we identify forms of LHCII with different fluorescence intensities and excited-state lifetimes. The distinct forms may be associated with different energy dissipation mechanisms in the energy transfer chain. Changes of relative populations in response to pH and carotenoid composition are observed, which may extend our understanding of the molecular mechanisms of photoprotection.

Paper Details

Date Published: 9 March 2015
PDF: 5 pages
Proc. SPIE 9331, Single Molecule Spectroscopy and Superresolution Imaging VIII, 933109 (9 March 2015); doi: 10.1117/12.2083628
Show Author Affiliations
Hsiang-Yu Yang, Stanford Univ. (United States)
Gabriela S. Schlau-Cohen, Stanford Univ. (United States)
Michal Gwizdala, Vrije Univ. Amsterdam (Netherlands)
Tjaart Krüger, Univ. of Pretoria (South Africa)
Pengqi Xu, Vrije Univ. Amsterdam (Netherlands)
Roberta Croce, Vrije Univ. Amsterdam (Netherlands)
Rienk van Grondelle, Vrije Univ. Amsterdam (Netherlands)
W. E. Moerner, Stanford Univ. (United States)

Published in SPIE Proceedings Vol. 9331:
Single Molecule Spectroscopy and Superresolution Imaging VIII
Jörg Enderlein; Ingo Gregor; Zygmunt Karol Gryczynski; Rainer Erdmann; Felix Koberling, Editor(s)

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