title: A permanent ion binding site located between two gates of the Shaker K+ channel.
abstract: K+ channels can be occupied by multiple permeant ions that appear to bind at discrete locations in the conduction pathway. Neither the molecular nature of the binding sites nor their relation to the activation or inactivation gates that control ion flow are well understood. We used the permeant ion Ba2+ as a K+ analog to probe for K+ ion binding sites and their relationship to the activation and inactivation gates. Our data are consistent with the existence of three single-file permeant-ion binding sites: one deep site, which binds Ba2+ with high affinity, and two more external sites whose occupancy influences Ba2+ movement to and from the deep site. All three sites are accessible to the external solution in channels with a closed activation gate, and the deep site lies between the activation gate and the C-type inactivation gate. We identify mutations in the P-region that disrupt two of the binding sites, as well as an energy barrier between the sites that may be part of the selectivity filter.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley 94720-3200, USA.
authors.forename: R E
authors.initials: RE
authors.lastname: Harris
authors.forename: H P
authors.initials: HP
authors.lastname: Larsson
authors.forename: E Y
authors.initials: EY
authors.lastname: Isacoff
mesh_terms: D000818:Animals; D001464:Barium / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D055592:Biophysical Phenomena; D001703:Biophysics; D004563:Electrochemistry; D005260:Female; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007700:Kinetics; D008564:Membrane Potentials; D008954:Models, Biological; D009865:Oocytes / Q000378:metabolism; D017354:Point Mutation; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D051637:Shaker Superfamily of Potassium Channels; D014982:Xenopus laevis
chemical_list: D015221:Potassium Channels; D011994:Recombinant Proteins; D051637:Shaker Superfamily of Potassium Channels; D001464:Barium; D011188:Potassium