1. D. A. Doyle, R. A. Pfuetzner, A. Kuo, and R. MacKinnon are in the Laboratory of Molecular Neurobiology and Biophysics and the Howard Hughes Medical Institute, Rockefeller University, 1230 York Avenue, New York, NY 10021, USA. J. M. Cabral and J. M. Gulbis are in the Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University, 1230 York Avenue, New York, NY 10021, USA. S. L. Cohen and B. T. Chait are in the Laboratory of Mass Spectrometry and Gaseous Ion Chemistry, Rockefeller...