Bichet Delphine, Grabe Michael, Jan Yuh Nung, Jan Lily Yeh
Departments of Physiology and Biochemistry and Howard Hughes Medical Institute, University of California, San Francisco, CA 94143.
Proc Natl Acad Sci U S A. 2006 Sep 26;103(39):14355-60. doi: 10.1073/pnas.0606660103. Epub 2006 Sep 18.
Potassium channels are membrane proteins that allow the passage of potassium ions at near diffusion rates while severely limiting the flux of the slightly smaller sodium ions. Although studies thus far have focused on the narrowest part of the channel, known as the selectivity filter, channels are long pores with multiple ions that traverse the selectivity filter, the water-filled central cavity, and the rest of the pore formed by cytoplasmic domains. Here, we present experimental analyses on Kir3.2 (GIRK2), a G protein-activated inwardly rectifying potassium (Kir) channel, showing that a negative charge introduced at a pore-facing position in the cavity (N184) below the selectivity filter restores both K(+) selectivity and inward rectification properties to the nonselective S177W mutant channel. Molecular modeling demonstrates that the negative residue has no effect on the geometry of the selectivity filter, suggesting that it has a local effect on the cavity ion. Moreover, restoration of selectivity does not depend on the exact location of the charge in the central cavity as long as this residue faces the pore, where it is in close contact with permeant ions. Our results indicate that interactions between permeant ions and the channel cavity can influence ion selectivity and channel block by means of an electrostatic effect.
钾通道是一种膜蛋白，它能使钾离子以接近扩散的速率通过，同时严重限制稍小的钠离子的通量。尽管迄今为止的研究都集中在通道最狭窄的部分，即所谓的选择性过滤器，但通道是长孔，有多个离子穿过选择性过滤器、充满水的中央腔以及由细胞质结构域形成的孔的其余部分。在这里，我们展示了对Kir3.2（GIRK2）的实验分析，Kir3.2是一种G蛋白激活的内向整流钾（Kir）通道，结果表明在选择性过滤器下方腔内面向孔的位置（N184）引入的负电荷恢复了非选择性S177W突变通道的K(+)选择性和内向整流特性。分子建模表明，负性残基对选择性过滤器的几何形状没有影响，这表明它对腔内离子有局部作用。此外，只要该残基面向孔并与渗透离子紧密接触，选择性的恢复不取决于电荷在中央腔内的确切位置。我们的结果表明，渗透离子与通道腔之间的相互作用可以通过静电效应影响离子选择性和通道阻断。
