How reduced excitonic coupling enhances light harvesting in the main photosynthetic antennae of diatoms
Loading...
Date
Authors
Kruger, T.P.J. (Tjaart)
Malý, Pavel
Alexandre, Maxime T.A.
Mančal, Tomáš
Büchel, Claudia
Van Grondelle, Rienk
Journal Title
Journal ISSN
Volume Title
Publisher
National Academy of Sciences
Abstract
Strong excitonic interactions are a key design strategy in photosynthetic light harvesting, expanding the spectral cross-section for light absorption and creating considerably faster and more robust excitation energy transfer. These molecular excitons are a direct result of exceptionally densely packed pigments in photosynthetic proteins. The main light-harvesting complexes of diatoms, known as fucoxanthin–chlorophyll proteins (FCPs), are an exception, displaying surprisingly weak excitonic coupling between their chlorophyll (Chl) a’s, despite a high pigment density. Here, we show, using single-molecule spectroscopy, that the FCP complexes of Cyclotella meneghiniana switch frequently into stable, strongly emissive states shifted 4–10 nm toward the red. A few percent of isolated FCPa complexes and ∼20% of isolated FCPb complexes, on average, were observed to populate these previously unobserved states, percentages that agree with the steady-state fluorescence spectra of FCP ensembles. Thus, the complexes use their enhanced sensitivity to static disorder to increase their light-harvesting capability in a number of ways. A disordered exciton model based on the structure of the main plant light-harvesting complex explains the red-shifted emission by strong localization of the excitation energy on a single Chl a pigment in the terminal emitter domain due to very specific pigment orientations. We suggest that the specific construction of FCP gives the complex a unique strategy to ensure that its light-harvesting function remains robust in the fluctuating protein environment despite limited excitonic interactions.
Description
Keywords
Fucoxanthin–chlorophyll proteins (FCPs), Chlorophyll (Chl), Photosynthetic excitons, Single-molecule spectroscopy, Light-harvesting complexes (LHCs), Protein disorder
Sustainable Development Goals
Citation
Kruger, T.P.J., Maly, P., Alexandre, M.T.A. et al. 2017, 'How reduced excitonic coupling enhances light harvesting in the main photosynthetic antennae of diatoms', Proceedings of the National Academy of Sciences of the United States of America, vol. 114, no. 52, pp. E11063-E11071.