1. Department of Biochemistry and Molecular Biology, Consortium for Advanced Radiation Sources, and Institute for Biophysical Dynamics, The University of Chicago, 920 East 58th Street, Chicago, Illinois 60637, Institut de Biologie Structurale Jean-Pierre Ebel, UMR 9015, 41 Avenue Jules Horowitz, 38027 Grenoble Cedex 1, France, European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex, France, and Department of Microbiology, E. C. Slater Institute, BioCentrum, University of Amsterdam, Nieuwe...