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Crystal structure of an ACh-binding protein reveals the ligand-binding domain of nicotinic receptors

Abstract

Pentameric ligand gated ion-channels, or Cys-loop receptors, mediate rapid chemical transmission of signals. This superfamily of allosteric transmembrane proteins includes the nicotinic acetylcholine (nAChR), serotonin 5-HT3, γ-aminobutyric-acid (GABAA and GABAC) and glycine receptors. Biochemical and electrophysiological information on the prototypic nAChRs is abundant but structural data at atomic resolution have been missing. Here we present the crystal structure of molluscan acetylcholine-binding protein (AChBP), a structural and functional homologue of the amino-terminal ligand-binding domain of an nAChR α-subunit. In the AChBP homopentamer, the protomers have an immunoglobulin-like topology. Ligand-binding sites are located at each of five subunit interfaces and contain residues contributed by biochemically determined ‘loops’ A to F. The subunit interfaces are highly variable within the ion-channel family, whereas the conserved residues stabilize the protomer fold. This AChBP structure is relevant for the development of drugs against, for example, Alzheimer’s disease and nicotine addiction.

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Figure 1: Sequence alignment of AChBP with pentameric ligand-gated ion channels (LGICs).
Figure 2: The pentameric structure of AChBP.
Figure 3: Overview of the AChBP protomer structure.
Figure 4: The ligand-binding site.
Figure 5: Dimer interface.
Figure 6: Conservation in the pentameric LGIC superfamily.

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Acknowledgements

We thank R. van der Schors for mass spectrometry; R. van Elk for HEPES binding assays; A. Perrakis and U. Gohlke for helpful suggestions; M. Lamers for help with figure preparation; and beam line scientists at ESRF and EMBL outstations Hamburg and Grenoble, in particular W. Rypniewski and G. Leonard for assistance during data collection. Nederlandse Organisatie voor Wetenschappelijk Onderzoek-Chemische Wetenschappen and Stichting voor de Technische Wetenschappen are acknowledged for financial support.

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Correspondence to Titia K. Sixma.

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Brejc, K., van Dijk, W., Klaassen, R. et al. Crystal structure of an ACh-binding protein reveals the ligand-binding domain of nicotinic receptors. Nature 411, 269–276 (2001). https://doi.org/10.1038/35077011

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