Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 286, Issue 48, Pages 41801-41811Publisher
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DOI: 10.1074/jbc.M111.278531
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Funding
- Ministry of Education, Culture, Sports, Science and Technology of Japan [22136002]
- [23590301]
- Grants-in-Aid for Scientific Research [22136001, 23590301, 22136002] Funding Source: KAKEN
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Ion channels gate at membrane-embedded domains by changing their conformation along the ion conduction pathway. Inward rectifier K+ (Kir) channels possess a unique extramembrane cytoplasmic domain that extends this pathway. However, the relevance and contribution of this domain to ion permeation remain unclear. By qualitative x-ray crystallographic analysis, we found that the pore in the cytoplasmic domain of Kir3.2 binds cations in a valency-dependent manner and does not allow the displacement of Mg2+ by monovalent cations or spermine Electrophysiological analyses revealed that the cytoplasmic pore of Kir3.2 selectively binds positively charged molecules and has a higher affinity for Mg2+ when it has a low probability of being open. The selective blocking of chemical modification of the side chain of pore-facing residues by Mg2+ indicates that the mode of binding of Mg2+ is likely to be similar to that observed in the crystal structure. These results indicate that the Kir3.2 crystal structure has a closed conformation with a negative electrostatic field potential at the cytoplasmic pore, the potential of which may be controlled by conformational changes in the cytoplasmic domain to regulate ion diffusion along the pore.
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