Hydration valve controlled non-selective conduction of Na(+) and K(+) in the NaK channel.
The Na(+) and K(+) channels are essential to neural signaling, but our current knowledge at the atomic level is mainly limited to the conducting mechanism of K(+). Unlike a K(+) channel having four equivalent K(+)-binding sites in its selectivity filter, a NaK channel has a vestibule in the middle part of its selectivity filter, and can conduct both Na(+) and K(+) ions. However, the underlying mechanism for non-selective ion conduction in NaK remains elusive. Here we find four small grottos connecting with the vestibule of the NaK selectivity filter, which form a vestibule-grotto complex perpendicular to the filter pore with a few water molecules within it. It is shown that two or more of the water molecules coming to the vestibule to coordinate the cation are necessary for conducting both Na(+) and K(+) ions, while only one water molecule in the vestibule will obstruct ion permeation. Thus, the complex with the aid of interior water movement forms a dynamic hydration valve which is flexible in conveying different cations through the vestibule. Similar exquisite hydration valve mechanisms are expected to be utilized by other non-selective cation channels, and the results should shed new light on the importance of water in neural signaling.
Shen
Rong
R
Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China.
Guo
Wanlin
W
Zhong
Wenyu
W
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D017136:Ion Transport; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D015398:Signal Transduction; D014867:Water / Q000737:chemistry
D001426:Bacterial Proteins; D015221:Potassium Channels; C107790:prokaryotic potassium channel; D014867:Water