Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States of America, Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States of America.|Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States of America.|Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States of America.|Center for Structural Biology, Department of Chemistry, Vanderbilt University, Nashville, Tennessee, United States of America.|Department of Physiology and Membrane Biology, University of California, Davis, Davis, California, United States of America.|Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, Israel.|Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States of America.