The dynamics of photosynthetic light harvesting: from ultrafast energy transfer to single-molecule conformational fluctuations
In photosynthetic light harvesting, organisms simultaneously achieve two seemingly opposite goals: 1) they convert photoenergy to chemical energy with near unity quantum efficiency; and 2) they safely dissipate excess photoenergy to avoid photodamage. Part of how photosynthetic organisms balance these two goals is through dynamics occurring on timescales spanning more than fifteen decades. On a femtosecond timescale, the remarkable quantum efficiency is achieved by energy rapidly transferring through networks of pigment-protein complexes in order to reach a central location to initiate photochemistry. We have used 2D electronic spectroscopy to map out the energy transfer dynamics through the most ubiquitous pigment-protein complex, LHCII. We determine energy transfers through LHCII via two parallel pathways, which contain previously unresolved sub-100 fs energy transfer steps. On a second timescale, the protein fluctuates between different functional conformations, which appear as an averaged value in ensemble measurements. We use a novel solution-phase (non-perturbative) single-molecule technique, the Anti-Brownian ELectrokinetic (ABEL) trap, to circumvent this ensemble averaging. In this way, we determine and characterize the conformational dynamics for the primary antenna pigment protein complex from purple bacteria, LH2. These experiments reveal that LH2 complexes exhibit a photoactivated, reversible switch to a state with increased quenching of photoenergy, which may be part of the organism's adaptation to the fluctuating intensity of sunlight. In this talk, the results presented will illustrate how the combination of 2D spectroscopy and single-molecule spectroscopy is a powerful experimental approach to elucidate the sophisticated molecular machinery that underlies photosynthetic light harvesting.
|日 時||2013年4月16日（火）16:00 ～|
|場 所||分子科学研究所 実験棟3階 301号室 アクセスマップ|
|題 目||The dynamics of photosynthetic light harvesting: from ultrafast energy transfer to single-molecule conformational fluctuations|
|講演者||Dr. Gabriela Schlau-Cohen (Department of Chemistry, Stanford University)|