Heterogeneous ultrafast relaxation in photosynthetic light-harvesting proteins

Speaker
  • Associate Professor of Chemistry, Massachusetts Institution of Technology
    Biography
      Gabriela Schlau-Cohen is an Associate Professor in the Department of Chemistry at the Massachusetts Institute of Technology. Her research group uses single-molecule spectroscopy and ultrafast spectroscopy to explore the energetic and structural dynamics of biological and bio-inspired systems. In particular, she has developed and applied tools to uncover the conformational and photophysical mechanisms of photosynthetic light harvesting and its regulation.

      She joined the faculty of MIT in 2015. Prior to MIT, she was a Postdoctoral Fellow of the Center for Molecular Analysis and Design at Stanford University, where she worked with Prof. W.E. Moerner. Dr. Schlau-Cohen received her PhD in Physical Chemistry in 2011 from the University of California, Berkeley, where she worked in the lab of Prof. Graham Fleming as an AAUW American Fellow. She received a B.S. with honors in Chemical Physics in 2003 from Brown University. She is the recipient of a NIH Director's New Innovator Award, the Beckman Young Investigator Award, the Smith Family Award for Excellence in Biomedical Research, the Sloan Research Fellowship in Chemistry and she was selected as a CIFAR Azrieli Global Scholar.

    Abstract

    In photosynthesis, solar energy capture to conversion occurs with a remarkable near-unity quantum efficiency through energy transport across a network of chromophore-containing proteins. Thermal fluctuations of these proteins lead to changes in the intermolecular interactions that drive energy transport. Despite this variation, high efficiency of transport is maintained. Both the extent to which the dynamics of energy transport vary and how the efficiency is robust to variation remain unclear. Previous measurements either lacked the temporal resolution required or the sensitivity to measure individual proteins, and thus averaged over the fluctuations. Here, we describe a new experiment, single-molecule pump-probe (SM2P) spectroscopy, that measures excited-state dynamics with femtosecond time resolution in single proteins. We demonstrate the power of this technique on cyanobacterial light-harvesting subunits. Our experiments reveal heterogeneous timescales of vibrational relaxation, yet a narrow distribution of energy transfer timescales. These results suggest the protein design serves to tightly regulate energy transfer despite fluctuations of its structure.


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