1. School of Physics and Astronomy, Faculty of Engineering and Physical Sciences, University of Leeds, Leeds LS2 9JT, U.K.
2. Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, U.K.
3. School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, U.K.
4. ISIS Neutron and Muon Spallation Source, STFC Rutherford Appleton Laboratory, Oxfordshire OX11 0QX, U.K.