The activation gate of a voltage-gated K+ channel can be trapped in the open state by an intersubunit metal bridge.
Voltage-activated K+ channels are integral membrane proteins containing a potassium-selective transmembrane pore gated by changes in the membrane potential. This activation gating (opening) occurs in milliseconds and involves a gate at the cytoplasmic side of the pore. We found that substituting cysteine at a particular position in the last transmembrane region (S6) of the homotetrameric Shaker K+ channel creates metal binding sites at which Cd2+ ions can bind with high affinity. The bound Cd2+ ions form a bridge between the introduced cysteine in one channel subunit and a native histidine in another subunit, and the bridge traps the gate in the open state. These results suggest that gating involves a rearrangement of the intersubunit contacts at the intracellular end of S6. The recently solved structure of a bacterial K+ channel shows that the S6 homologs cross in a bundle, leaving an aperture at the bundle crossing. In the context of this structure, the metal ions form a bridge between a cysteine above the bundle crossing and a histidine below the bundle crossing in a neighboring subunit. Our results suggest that gating occurs at the bundle crossing, possibly through a change in the conformation of the bundle itself.
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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D019943:Amino Acid Substitution; D001665:Binding Sites; D002104:Cadmium / Q000378:metabolism* / Q000494:pharmacology; D002460:Cell Line; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D007700:Kinetics; D046911:Macromolecular Substances; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D015221:Potassium Channels / Q000737:chemistry / Q000502:physiology*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D051637:Shaker Superfamily of Potassium Channels; D014162:Transfection
D046911:Macromolecular Substances; D015221:Potassium Channels; D011994:Recombinant Proteins; D051637:Shaker Superfamily of Potassium Channels; D002104:Cadmium