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Ion Selectivity in a Semisynthetic K+ Channel Locked in the Conductive Conformation
Francis I. Valiyaveetil,*
Manuel Leonetti,
Tom W. Muir,
Roderick MacKinnon
Abstract:
Potassium channels are K+-selective protein pores in cell membrane.The selectivity filter is the functional unit that allows K+channels to distinguish potassium (K+) and sodium (Na+) ions.The filter's structure depends on whether K+ or Na+ ions arebound inside it. We synthesized a K+ channel containing theD-enantiomer of alanine in place of a conserved glycine andfound by x-ray crystallography that its filter maintains theK+ (conductive) structure in the presence of Na+ and very lowconcentrations of K+. This channel conducts Na+ in the absenceof K+ but not in the presence of K+. These findings demonstratethat the ability of the channel to adapt its structure differentlyto K+ and Na+ is a fundamental aspect of ion selectivity, asis the ability of multiple K+ ions to compete effectively withNa+ for the conductive filter.
Laboratories of Molecular Neurobiology and Biophysics and Synthetic Protein Chemistry, Rockefeller University and Howard Hughes Medical Institute, 1230 York Avenue, New York, NY 10021, USA, and Department of Biology, Ecole Normale Superieure, 46 rue d'Ulm, 75005 Paris, France.
* Present address: Department of Physiology and Pharmacology,Oregon Health Sciences University, 3181 SW Sam Jackson ParkRoad, Mail Code L334, Portland, OR 97239, USA.
To whom correspondence should be addressed. E-mail: mackinn{at}rockefeller.edu (R.M.), muirt{at}rockefeller.edu (T.W.M.)
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