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Coupling of light-induced electron transfer to proton uptake in photosynthesis

Nature Structural & Molecular Biology volume 10, pages 637–644 (2003)Cite this article

Abstract

Light energy is transformed into chemical energy in photosynthesis by coupling a light-induced electron transfer to proton uptake. The resulting proton gradient drives ATP synthesis. In this study, we monitored the light-induced reactions in a 100-kDa photosynthetic protein from 30 ns to 35 s by FTIR difference spectroscopy. The results provide detailed mechanistic insights into the electron and proton transfer reactions of the QA to QB transition: reduction of QA in picoseconds induces protonation of histidines, probably of His126 and His128 in the H subunit at the entrance of the proton uptake channel, and of Asp210 in the L subunit inside the channel at 12 μs and 150 μs. This seems to be a prerequisite for the reduction of QB, mainly at 150 μs. QA− is reoxidized at 1.1 ms, and a proton is transferred from Asp210 to Glu212 in the L subunit, the proton donor to QB−. Notably, our data indicate that QB is not reduced directly by QA− but presumably through an intermediary electron donor.

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Figure 1: Light-induced electron transfer from P to QA takes place within 200 ps via overlapping prosthetic groups.
Figure 2: Three-dimensional representation of the light-induced IR absorbance changes in the photosynthetic reaction center of Rb. sphaeroides between 1,900 and 1,000 cm−1 with 30-ns time resolution and 7-cm−1 spectral resolution as revealed by global fit analysis.
Figure 3: Absorbance changes of P+, QB− and QA− marker bands.
Figure 4: On an expanded scale the QA−QB → QAQB− transition is shown from 1 μs to 10 ms.
Figure 5: Amplitude spectra from 1,900 to 1,000 cm−1 for the three kinetic phases.
Figure 6: Comparison of wild-type and D210N (L) mutant kinetics in the QA−QB → QAQB− transition.
Figure 7: FTIR results in the context of the structural model (PDB entry 1AIG)6.

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Acknowledgements

This work was financially supported by the Deutsche Forschungsgemeinschaft. We thank T.A. Egorova-Zachernyuk for providing RC sample material and D. Oesterhelt for providing the Rb. sphaeroides deletion strain pufΔLMX21. We thank C. Fichtner for help in mutagenesis, C. Kandt for preparing Figures 1 and 7 and R. Goody for careful reading of the manuscript.

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  1. Lehrstuhl für Biophysik, Ruhr-Universität Bochum, Postfach 102148, Bochum, 44780, Germany

    André Remy & Klaus Gerwert

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Correspondence to Klaus Gerwert.

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Remy, A., Gerwert, K. Coupling of light-induced electron transfer to proton uptake in photosynthesis. Nat Struct Mol Biol 10, 637–644 (2003). https://doi.org/10.1038/nsb954

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