Light-Induced Structural Changes in a Photosynthetic Reaction Center Caught by Laue Diffraction

Photosynthetic reaction centers convert the energy content of light into a transmembrane potentialdifference and so provide the major pathway for energy input into the biosphere. We appliedtime-resolved Laue diffraction to study light-induced conformational changes in the photosyntheticreaction center complex ofBlastochloris viridis. The side chain of TyrL162, which lies adjacent to thespecial pair of bacteriochlorophyll molecules that are photooxidized in the primary light conversion eventof photosynthesis, was observed to move 1.3 angstroms closer to the special pair after photoactivation.Free energy calculations suggest that this movement results from the deprotonation of this conservedtyrosine residue and provides a mechanism for stabilizing the primary charge separation reactions ofphotosynthesis