title: The barium site in a potassium channel by x-ray crystallography.
abstract: X-ray diffraction data were collected from frozen crystals (100 degrees K) of the KcsA K(+) channel equilibrated with solutions containing barium chloride. Difference electron density maps (F(barium) - F(native), 5.0 A resolution) show that Ba(2+) resides at a single location within the selectivity filter. The Ba(2+) blocking site corresponds to the internal aspect (adjacent to the central cavity) of the "inner ion" position where an alkali metal cation is found in the absence of the blocking Ba(2+) ion. The location of Ba(2+) with respect to Rb(+) ions in the pore is in good agreement with the findings on the functional interaction of Ba(2+) with K(+) (and Rb(+)) in Ca(2+)-activated K(+) channels (Neyton, J., and C. Miller. 1988. J. Gen. Physiol. 92:549-567). Taken together, these structural and functional data imply that at physiological ion concentrations a third ion may interact with two ions in the selectivity filter, perhaps by entering from one side and displacing an ion on the opposite side.
authors.affiliation: Howard Hughes Medical Institute, Laboratory of Molecular Neurobiology and Biophysics, The Rockefeller University, New York, New York 10021, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Jiang
authors.forename: R
authors.initials: R
authors.lastname: MacKinnon
mesh_terms: D001426:Bacterial Proteins; D001464:Barium / Q000378:metabolism / Q000494:pharmacology*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins; D015221:Potassium Channels; C107790:prokaryotic potassium channel; D001464:Barium