%AHiggins, Jacob%ALloyd, Lawson%ASohail, Sara%AAllodi, Marco%AOtto, John%ASaer, Rafael%AWood, Ryan%AMassey, Sara%ATing, Po-Chieh%ABlankenship, Robert%AEngel, Gregory%BJournal Name: Proceedings of the National Academy of Sciences; Journal Volume: 118; Journal Issue: 11; Related Information: CHORUS Timestamp: 2021-03-09 15:50:55 %D2021%IProceedings of the National Academy of Sciences; None %JJournal Name: Proceedings of the National Academy of Sciences; Journal Volume: 118; Journal Issue: 11; Related Information: CHORUS Timestamp: 2021-03-09 15:50:55 %K %MOSTI ID: 10216811 %PMedium: X %TPhotosynthesis tunes quantum-mechanical mixing of electronic and vibrational states to steer exciton energy transfer %X
Photosynthetic species evolved to protect their light-harvesting apparatus from photoxidative damage driven by intracellular redox conditions or environmental conditions. The Fenna–Matthews–Olson (FMO) pigment–protein complex from green sulfur bacteria exhibits redox-dependent quenching behavior partially due to two internal cysteine residues. Here, we show evidence that a photosynthetic complex exploits the quantum mechanics of vibronic mixing to activate an oxidative photoprotective mechanism. We use two-dimensional electronic spectroscopy (2DES) to capture energy transfer dynamics in wild-type and cysteine-deficient FMO mutant proteins under both reducing and oxidizing conditions. Under reducing conditions, we find equal energy transfer through the exciton 4–1 and 4–2-1 pathways because the exciton 4–1 energy gap is vibronically coupled with a bacteriochlorophyll-