Journal
JOURNAL OF GENERAL PHYSIOLOGY
Volume 115, Issue 3, Pages 269-272Publisher
ROCKEFELLER UNIV PRESS
DOI: 10.1085/jgp.115.3.269
Keywords
potassium channel; barium; ion channel; ion selectivity; ion conduction
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Funding
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R01GM047400] Funding Source: NIH RePORTER
- NIGMS NIH HHS [R01 GM047400, GM47400] Funding Source: Medline
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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 Angstrom resolution) show that Ba2+ resides at a single location within the selectivity filter. The Ba2+ 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 Ba2+ ion. The location of Ba2+ with respect to Rb+ ions in the pore is in good agreement with the findings on the functional interaction of Ba2+ with K+ (and Rb+) in Ca2+-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.
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