Biophysics Program, Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA.|Biophysics Program, Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA.|Biophysics Program, Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA.|Biophysics Program, Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA.