The nicotinic acetylcholine (ACh) receptor converts transiently to an open-channel form when activated by ACh released into the synaptic cleft. We describe here the conformational change underlying ...The nicotinic acetylcholine (ACh) receptor converts transiently to an open-channel form when activated by ACh released into the synaptic cleft. We describe here the conformational change underlying this event, determined by electron microscopy of ACh-sprayed and freeze-trapped postsynaptic membranes. ACh binding to the α subunits triggers a concerted rearrangement in the ligand-binding domain, involving an ~1-Å outward displacement of the extracellular portion of the β subunit where it interacts with the juxtaposed ends of α-helices shaping the narrow membrane-spanning pore. The β-subunit helices tilt outward to accommodate this displacement, destabilising the arrangement of pore-lining helices, which in the closed channel bend inward symmetrically to form a central hydrophobic gate. Straightening and tangential motion of the pore-lining helices effect channel opening by widening the pore asymmetrically and increasing its polarity in the region of the gate. The pore-lining helices of the α(γ) and δ subunits, by flexing between alternative bent and straight conformations, undergo the greatest movements. This coupled allosteric transition shifts the structure from a tense (closed) state toward a more relaxed (open) state.
EMDB-2071: Gating movement in acetylcholine receptor analysed by time-resolved electron cryo-microscopy PDB-4aq5: Gating movement in acetylcholine receptor analysed by time-resolved electron cryo-microscopy (closed class) Method: EM (helical sym.) / Resolution: 6.2 Å
EMDB-2072: Gating movement in acetylcholine receptor analysed by time-resolved electron cryo-microscopy PDB-4aq9: Gating movement in acetylcholine receptor analysed by time- resolved electron cryo-microscopy (open class) Method: EM (helical sym.) / Resolution: 6.2 Å
Source
torpedo marmorata (marbled electric ray)
Keywords
MEMBRANE PROTEIN / FREEZE-TRAPPING / ASYMMETRIC GATING / ALLOSTERIC MECHANISM
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Keywords
torpedo marmorata (marbled electric ray)