1. Astbury Centre for Structural Molecular Biology and School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, U.K.
2. Physik-Department, Lehrstuhl für Biophysik E22, Technische Universität München, D-85748 Garching, Germany
3. Hamburg Centre of Ultrafast Imaging and Institute for Nanostructure and Solid State Physics, Universität Hamburg, D-22761 Hamburg, Germany