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Coupling of agonist binding to channel gating in an ACh-binding protein linked to an ion channel

Abstract

Neurotransmitter receptors from the Cys-loop superfamily couple the binding of agonist to the opening of an intrinsic ion pore in the final step in rapid synaptic transmission. Although atomic resolution structural data have recently emerged for individual binding1 and pore domains2, how they are linked into a functional unit remains unknown. Here we identify structural requirements for functionally coupling the two domains by combining acetylcholine (ACh)-binding protein, whose structure was determined at atomic resolution1, with the pore domain from the serotonin type-3A (5-HT3A) receptor. Only when amino-acid sequences of three loops in ACh-binding protein are changed to their 5-HT3A counterparts does ACh bind with low affinity characteristic of activatable receptors, and trigger opening of the ion pore. Thus functional coupling requires structural compatibility at the interface of the binding and pore domains. Structural modelling reveals a network of interacting loops between binding and pore domains that mediates this allosteric coupling process.

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Figure 1: Design and structural model of receptor chimaeras.
Figure 2: ACh-activated currents through chimaeric receptors.
Figure 3: ACh-activated single-channel currents through chimaeric receptors at different membrane potentials.

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Acknowledgements

This work was supported by grants from the National Institutes of Health, UNS, ANPCyT and F. Antorchas, Argentina.

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Correspondence to Steven M. Sine.

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Bouzat, C., Gumilar, F., Spitzmaul, G. et al. Coupling of agonist binding to channel gating in an ACh-binding protein linked to an ion channel. Nature 430, 896–900 (2004). https://doi.org/10.1038/nature02753

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