Single-molecule exploration of photoprotective mechanisms in light-harvesting complexes

Hsiang Yu Yang, Gabriela S. Schlau-Cohen, Michal Gwizdala, Tjaart Krüger, Pengqi Xu, Roberta Croce, Rienk Van Grondelle, W. E. Moerner

Research output: Chapter in Book / Report / Conference proceedingConference contributionAcademicpeer-review


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.

Original languageEnglish
Title of host publicationSingle Molecule Spectroscopy and Superresolution Imaging VIII
ISBN (Electronic)9781628414219
Publication statusPublished - 2015
EventSingle Molecule Spectroscopy and Superresolution Imaging VIII - San Francisco, United States
Duration: 7 Feb 20158 Feb 2015


ConferenceSingle Molecule Spectroscopy and Superresolution Imaging VIII
Country/TerritoryUnited States
CitySan Francisco


  • Anti-Brownian ELectrokinetic trap
  • photoprotection
  • single molecules


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