期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 101, 期 9, 页码 3248-3252出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0308743101
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资金
- NIMH NIH HHS [R01 MH061506, MH061506] Funding Source: Medline
- NINDS NIH HHS [NS031557, R01 NS031557] Funding Source: Medline
A universal property of ion channels is their ability to alternate stochastically between two permeation states, open and closed. This behavior is thought to be controlled by a steric gate, a structure that physically impedes ion flow in the closed state and moves out of the way during channel opening. Experiments employing macroscopic currents in the Shaker K channel have suggested a cytoplasmic localization for the gate. Crystallographic structures of the KcsA K channel indeed reveal a cytoplasmic constriction, implying that the gate and selectivity filter are localized to opposite ends of the permeation pathway. However, analysis of K channel subconductance behavior has suggested a strict coupling between channel opening (gating) and permeation. The idea that the selectivity filter is the gate was therefore investigated by using Monte Carlo simulations. Gating is accomplished by allowing the filter to alternate stochastically between two conformations: a high-affinity state, which selectively binds K ions (but not Na ions) and traps them, and a completely nonselective, low-affinity state, which allows both Na and K ions to permeate. The results of these simulations indicate that affinity switching not only endows the selectivity filter with gating abilities, it also allows efficient permeation without jeopardizing ion selectivity. In this model, permeation and gating result from the same process.
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