X-ray free electron laser (XFEL) radiation is revolutionizing experimental approaches to structural biology. One area where XFEL radiation is expected to have a large impact is time-resolved structural studies of protein conformational changes. The femtosecond time-scale of XFEL pulses creates completely new possibilities for visualizing ultrafast structural changes in photosynthetic membrane protein complexes. In this presentation I will describe collaborative studies performed at the LCLS on the photosynthetic reaction centre of Bl. viridis, a highly conserved protein that is the work-horse of photosynthesis. Results from Time-Resolved Wide Angle X-ray Scattering (TR-WAXS) and Time-resolved Serial Femtosecond Crystallography

(TR-SFX) studies of this integral membrane protein suggest that conformational changes do occur on the picosecond time-scale. In the multi-photon regime we observed a protein quake: whereby the protein initially responds to energy deposited into buried chromophores through a structural deformation that grows on a time scale of picoseconds and is damped within tens of picoseconds. In the single-photon regime, structural changes were observed near the special pair (which is photo-oxidized following the absorption of a photon) and the menaquinone (which is reduced by the movement of an electron from the special pair) on the picosecond time-scale. These results provide new chemical insight into the major mechanism by which the energy of sunlight is directed into the biosphere.

Richard Neutze, Rob Dods, David Arnlund, Linda Johansson, Petra Båth.

University of Gothenburg, Sweden.

Anton Barty, Kenneth Beyerlein, Henry Chapman.

CFEL, DESY, Germany.

Sebastian Boutet, Daniel dePonte.

LCLS, USA.

Gerrit Groenhof

University of Jyväskylä, Finland.

Garrett Nelson, John Spence.

Arizona State University, USA.