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A Hydrophobic Gate in an Ion Channel: The Closed State of the Nicotinic Acetylcholine Receptor | | Oliver Beckstein
; Mark S. P. Sansom
; | | Date: |
15 Sep 2005 | | Subject: | Biomolecules; Subcellular Processes | q-bio.BM q-bio.SC | | Abstract: | The nicotinic acetylcholine receptor (nAChR) is the prototypic member of the `Cys-loop’ superfamily of ligand-gated ion channels which mediate synaptic neurotransmission, and whose other members include receptors for glycine, gamma-aminobutyric acid, and serotonin. Cryo-electron microscopy has yielded a three dimensional structure of the nAChR in its closed state. However, the exact nature and location of the channel gate remains uncertain. Although the transmembrane pore is constricted close to its center, it is not completely occluded. Rather, the pore has a central hydrophobic zone of radius about 0.3 nm. Model calculations suggest that such a constriction may form a hydrophobic gate, preventing movement of ions through a channel. We demonstrate that the hydrophobic constriction of the nAChR pore indeed forms a closed gate. Potential of mean force calculations reveal that the constriction presents a barrier of height ca. 9 kT to the permeation of ions, placing an upper bound on the closed channel conductance of 0.1 pS. A central location of the gate is consistent with recent mutational data. Thus, a 0.3 nm radius hydrophobic pore can form a functional barrier to the permeation of a 0.1 nm radius ion. | | Source: | arXiv, q-bio.BM/0509018 | | Services: | Forum | Review | PDF | Favorites | |
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