The ligand-sensitive gate of a potassium channel lies close to the selectivity filter
Proks P., Antcliff JF., Ashcroft FM.
Potassium channels selectively conduct K+ions across cell membranes and have key roles in cell excitability. Their opening and closing can be spontaneous or controlled by membrane voltage or ligand binding. We used Ba2+as a probe to determine the location of the ligand-sensitive gate in an inwardly rectifying K+channel (Kir6.2). To a K+channel, Ba2+and K+are of similar sizes, but Ba2+blocks the pore by binding within the selectivity filter. We found that internal Ba2+could still access its binding site when the channel was shut, which indicates that the ligand-sensitive gate lies above the Ba2+-block site, and thus within or above the selectivity filter. This is in marked contrast to the voltage-dependent gate of KVchannels, which is located at the intracellular mouth of the pore.