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Observation of robust energy transfer in the photosynthetic protein allophycocyanin using single-molecule pump–probe spectroscopy

Nature Chemistry volume 14, pages 153–159 (2022)Cite this article

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Abstract

Photosynthetic organisms convert sunlight to electricity with near unity quantum efficiency. Absorbed photoenergy transfers through a network of chromophores positioned within protein scaffolds, which fluctuate due to thermal motion. The resultant variation in the individual energy transfer steps has not yet been measured, and so how the efficiency is robust to this variation has not been determined. Here, we describe single-molecule pump–probe spectroscopy with facile spectral tuning and its application to the ultrafast dynamics of single allophycocyanin, a light-harvesting protein from cyanobacteria. We disentangled the energy transfer and energetic relaxation from nuclear motion using the spectral dependence of the dynamics. We observed an asymmetric distribution of timescales for energy transfer and a slower and more heterogeneous distribution of timescales for energetic relaxation, which was due to the impact of the protein environment. Collectively, these results suggest that energy transfer is robust to protein fluctuations, a prerequisite for efficient light harvesting.

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Fig. 1: SM2P experiments on APC.
Fig. 2: Distributions of energetic relaxation and energy transfer timescales for APC.
Fig. 3: Comparison of distributions of energy relaxation timescales.

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Data availability

The raw photon stream used to construct the single-molecule pump–probe traces and the corresponding fluorescence lifetime histograms are available at https://doi.org/10.5281/zenodo.5541825. Source data are provided with this paper.

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Acknowledgements

This work was supported by the National Institutes of Health Director’s New Innovator Award 1DP2GM128200-01 and a Beckman Young Investigator Award (G.S.S.-C.). R.M. acknowledges a National Science Foundation Graduate Research Fellowship. T.K. acknowledges a Japan Science and Technology Agency PRESTO (no. JPMJPR18G7) and a Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (no. 19H02665). G.S.S.-C. also acknowledges a Smith Family Award for Excellence in Biomedical Research, Sloan Research Fellowship in Chemistry and a CIFAR Global Scholar Award.

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Authors and Affiliations

  1. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA

    Raymundo Moya, Audrey C. Norris & Gabriela S. Schlau-Cohen

  2. Department of Life Science and Technology, Tokyo Institute of Technology, Tokyo, Japan

    Toru Kondo

  3. PRESTO, Japan Science and Technology Agency, Saitama, Japan

    Toru Kondo

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  1. Raymundo Moya
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  2. Audrey C. Norris
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  4. Gabriela S. Schlau-Cohen
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Contributions

R.M., T.K. and G.S.S.-C. conceived and designed the experiments. R.M. and A.C.N. performed the experiments. R.M. and G.S.S.-C. analysed the data. R.M., A.C.N. and G.S.S.-C. co-wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Gabriela S. Schlau-Cohen.

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The authors declare no competing interests.

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Peer review information Nature Chemistry thanks Pavel Malý, Tomas Polivka and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Single-molecule pump–probe experiments on C-phycocyanin.

(a) The structure of C-phycocyanin (Protein Data Bank ID Code 1GH0) is shown with a callout of a tetrapyrole chromophore (purple). (b) The corresponding absorption (solid) and emission (dashed) spectra are shown with the 610 nm excitation shown in blue. (c-f) Representative traces for C-phycocyanin with 610 nm excitation are with values of 125 ± 2, 503 ± 124, 113 ± 29, and 270 ± 51 fs, respectively. Errors given are the standard error of the maximum likelihood estimate.

Source data

Extended Data Fig. 2 Gaussian mixture model extracts two rate components.

The distributions of energy relaxation rates from the bright (top) and quenched (bottom) populations were fit to a two-component Gaussian mixture model, which is shown in dashed lines. All parameters of the Gaussian mixture model fit are given in Supplementary Table 4.

Source data

Supplementary information

Supplementary Information

Supplementary Figs. 1–19, Discussion, and experimental and theoretical methodology.

Source data

Source Data Fig. 1

Optical spectra and fluorescence time series.

Source Data Fig. 2

Numerical data for histograms.

Source Data Fig. 3

Numerical data for histograms.

Source Data Extended Data Fig. 1

Numerical data for histograms.

Source Data Extended Data Fig. 2

Optical spectra and fluorescence time series.

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Moya, R., Norris, A.C., Kondo, T. et al. Observation of robust energy transfer in the photosynthetic protein allophycocyanin using single-molecule pump–probe spectroscopy. Nat. Chem. 14, 153–159 (2022). https://doi.org/10.1038/s41557-021-00841-9

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