The pore helix is involved in stabilizing the open state of inwardly rectifying K+ channels.
Ion channels can be gated by various extrinsic cues, such as voltage, pH, and second messengers. However, most ion channels display extrinsic cue-independent transitions as well. These events represent spontaneous conformational changes of the channel protein. The molecular basis for spontaneous gating and its relation to the mechanism by which channels undergo activation gating by extrinsic cue stimulation is not well understood. Here we show that the proximal pore helix of inwardly rectifying (Kir) channels is partially responsible for determining spontaneous gating characteristics, affecting the open state of the channel by stabilizing intraburst openings as well as the bursting state itself without affecting K(+) ion-channel interactions. The effect of the pore helix on the open state of the channel is qualitatively similar to that of two well-characterized mutations at the second transmembrane domain (TM2), which stabilize the channel in its activated state. However, the effects of the pore helix and the TM2 mutations on gating were additive and independent of each other. Moreover, in sharp contrast to the two TM2 mutations, the pore helix mutation did not affect the functionality of the agonist-responsive gate. Our results suggest that in Kir channels, the bottom of the pore helix and agonist-induced conformational transitions at the TM2 ultimately stabilize via different pathways the open conformation of the same gate.
Alagem
Noga
N
Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
Yesylevskyy
Semen
S
Reuveny
Eitan
E
D000818:Animals; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D009154:Mutation; D009865:Oocytes / Q000737:chemistry / Q000502:physiology; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000737:chemistry / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry / Q000502:physiology*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; C484274:KCNJ5 protein, human; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D021122:Protein Subunits; D011994:Recombinant Proteins; D011188:Potassium