Equilibrium selectivity alone does not create K+-selective ion conduction in K+ channels

• Published in: Nature communications Vol. 4; no. 1; p. 2746
• Main Authors: Liu, Shian, Lockless, Steve W
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 2013
• Subjects: Amino Acid Sequence; Bacterial Proteins - physiology; Binding sites; Equilibrium; Ion Channel Gating - physiology; Models, Molecular; Molecular Sequence Data; Permeability; Potassium - metabolism; Potassium Channels - chemistry; Potassium Channels - metabolism; Potassium Channels - physiology; Protein Conformation
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms3746

Potassium (K(+)) channels are selective for K(+) over Na(+) ions during their transport across membranes. We and others have previously shown that tetrameric K(+) channels are primarily occupied by K(+) ions in their selectivity filters under physiological conditions, demonstrating the channel's intrinsic equilibrium preference for K(+) ions. Based on this observation, we hypothesize that the preference for K(+) ions over Na(+) ions in the filter determines its selectivity during ion conduction. Here, we ask whether non-selective cation channels, which share an overall structure and similar individual ion-binding sites with K(+) channels, have an ion preference at equilibrium. The variants of the non-selective Bacillus cereus NaK cation channel we examine are all selective for K(+) over Na(+) ions at equilibrium. Thus, the detailed architecture of the K(+) channel selectivity filter, and not only its equilibrium ion preference, is fundamental to the generation of selectivity during ion conduction.