Valiyaveetil Francis I, Leonetti Manuel, Muir Tom W, Mackinnon Roderick
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.
Science. 2006 Nov 10;314(5801):1004-7. doi: 10.1126/science.1133415.
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 are bound inside it. We synthesized a K+ channel containing the d-enantiomer of alanine in place of a conserved glycine and found by x-ray crystallography that its filter maintains the K+ (conductive) structure in the presence of Na+ and very low concentrations of K+. This channel conducts Na+ in the absence of K+ but not in the presence of K+. These findings demonstrate that the ability of the channel to adapt its structure differently to K+ and Na+ is a fundamental aspect of ion selectivity, as is the ability of multiple K+ ions to compete effectively with Na+ for the conductive filter.
钾通道是细胞膜中对钾离子具有选择性的蛋白质孔道。选择性过滤器是使钾通道能够区分钾离子（K⁺）和钠离子（Na⁺）的功能单元。过滤器的结构取决于其内部结合的是K⁺还是Na⁺离子。我们合成了一个用丙氨酸的d-对映体取代保守甘氨酸的钾通道，通过X射线晶体学发现，在存在Na⁺和极低浓度K⁺的情况下，其过滤器保持K⁺（导电）结构。该通道在没有K⁺时传导Na⁺，但在有K⁺时不传导。这些发现表明，通道对K⁺和Na⁺结构进行不同适应的能力是离子选择性的一个基本方面，多个K⁺离子与Na⁺有效竞争导电过滤器的能力也是如此。
