Equilibrium selectivity alone does not create K+-selective ion conduction in K+ channels.
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.
Department of Biology, Texas A&M University, College Station, TX 77843, USA.
Shian
S
Liu
Steve W
SW
Lockless
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D011487:Protein Conformation
D001426:Bacterial Proteins; D015221:Potassium Channels; C107790:prokaryotic potassium channel; D011188:Potassium