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Detection and trapping of intermediate states priming nicotinic receptor channel opening

Abstract

In the course of synaptic transmission in the brain and periphery, acetylcholine receptors (AChRs) rapidly transduce a chemical signal into an electrical impulse. The speed of transduction is facilitated by rapid ACh association and dissociation, suggesting a binding site relatively non-selective for small cations. Selective transduction has been thought to originate from the ability of ACh, over that of other organic cations, to trigger the subsequent channel-opening step. However, transitions to and from the open state were shown to be similar for agonists with widely different efficacies1,2,3. By studying mutant AChRs, we show here that the ultimate closed-to-open transition is agonist-independent and preceded by two primed closed states; the first primed state elicits brief openings, whereas the second elicits long-lived openings. Long-lived openings and the associated primed state are detected in the absence and presence of an agonist, and exhibit the same kinetic signatures under both conditions. By covalently locking the agonist-binding sites in the bound conformation, we find that each site initiates a priming step. Thus, a change in binding-site conformation primes the AChR for channel opening in a process that enables selective activation by ACh while maximizing the speed and efficiency of the biological response.

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Figure 1: Agonist-independent channel gating.
Figure 2: Covalent priming of the AChR.
Figure 3: Mutating residues linking binding and pore domains increases or decreases priming.
Figure 4: Primed model of AChR activation.

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Acknowledgements

We thank D. Johnson for computer programming, and C. Free for technical contributions. This work was supported by National Institutes of Health grant NS031744 (S.M.S.).

Author Contributions N.M., W.Y.L. and H.L.W. conducted the experiments; N.M., W.Y.L. and S.M.S. analysed the data; S.M.S. wrote the manuscript. All authors discussed the results and commented on the manuscript.

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Correspondence to Steven M. Sine.

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Mukhtasimova, N., Lee, W., Wang, HL. et al. Detection and trapping of intermediate states priming nicotinic receptor channel opening. Nature 459, 451–454 (2009). https://doi.org/10.1038/nature07923

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