The selectivity filter may act as the agonist-activated gate in the G protein-activated Kir3.1/Kir3.4 K+ channel.
The Kir3.1/Kir3.4 channel is activated by Gbetagamma subunits released on binding of acetylcholine to the M2 muscarinic receptor. A mechanism of channel opening, similar to that for the KcsA and Shaker K+ channels, has been suggested that involves translocation of pore lining transmembrane helices and the opening of an intracellular gate at the "bundle crossing" region. However, in the present study, we show that an extracellular gate at the selectivity filter is critical for agonist activation of the Kir3.1/Kir3.4 channel. Increasing the flexibility of the selectivity filter, by disrupting a salt bridge that lies directly behind the filter, abolished both selectivity for K+ and agonist activation of the channel. Other mutations within the filter that altered selectivity also altered agonist activation. In contrast, mutations within the filter that did not affect selectivity had little if any effect on agonist activation. Interestingly, mutation of bulky side chain phenylalanine residues at the bundle crossing also altered both agonist activation and selectivity. These results demonstrate a significant correlation between agonist activation and selectivity, which is determined by the selectivity filter, and suggests, therefore, that the selectivity filter may act as the agonist-activated gate in the Kir3.1/Kir3.4 channel.
Claydon
Thomas W
TW
School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom.
Makary
Samy Y
SY
Dibb
Katharine M
KM
Boyett
Mark R
MR
D000595:Amino Acid Sequence; D000818:Animals; D004594:Electrophysiology; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D010649:Phenylalanine / Q000737:chemistry; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012492:Salts / Q000494:pharmacology; D014981:Xenopus
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012492:Salts; D010649:Phenylalanine