Zhou Ming, MacKinnon Roderick
Howard Hughes Medical Institute and Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University, New York, NY 10021, USA.
J Mol Biol. 2004 May 7;338(4):839-46. doi: 10.1016/j.jmb.2004.03.020.
The selectivity filter of K(+) channels is comprised of a linear queue of four equal-spaced ion-binding sites spanning a distance of 12A. Each site is formed of eight oxygen atoms from the protein. The first three sites, numbered 1-3 from the extracellular side, are made of exclusively main-chain carbonyl oxygen atoms. The fourth site, closest to the intracellular side, is made of four main-chain carbonyl oxygen atoms and four threonine side-chain hydroxyl oxygen atoms. Here we characterize the effects of mutating the threonine to cysteine on the distribution of ions in the selectivity filter and on the conduction of ions through the filter. The mutation influences the occupancy of K(+) at sites 2 and 4 and it reduces the maximum rate of conduction in the limit of high K(+) concentration. The mutation does not affect the conduction of Rb(+). These results can be understood in the context of a conduction mechanism in which a pair of K ions switch between energetically balanced 1,3 and 2,4 configurations.
钾离子通道的选择性过滤器由四个等间距离子结合位点的线性队列组成，跨越12埃的距离。每个位点由蛋白质中的八个氧原子形成。前三个位点，从细胞外侧开始编号为1-3，仅由主链羰基氧原子构成。最靠近细胞内侧的第四个位点由四个主链羰基氧原子和四个苏氨酸侧链羟基氧原子构成。在此，我们描述了将苏氨酸突变为半胱氨酸对选择性过滤器中离子分布以及离子通过过滤器传导的影响。该突变影响位点2和4处钾离子的占据情况，并在高钾离子浓度极限下降低最大传导速率。该突变不影响铷离子的传导。这些结果可以在一种传导机制的背景下得到理解，即在该机制中，一对钾离子在能量平衡的1,3和2,4构型之间切换。
