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Ligand-binding domain of an α7-nicotinic receptor chimera and its complex with agonist

Abstract

The α7 acetylcholine receptor (AChR) mediates pre- and postsynaptic neurotransmission in the central nervous system and is a potential therapeutic target in neurodegenerative, neuropsychiatric and inflammatory disorders. We determined the crystal structure of the extracellular domain of a receptor chimera constructed from the human α7 AChR and Lymnaea stagnalis acetylcholine binding protein (AChBP), which shares 64% sequence identity and 71% similarity with native α7. We also determined the structure with bound epibatidine, a potent AChR agonist. Comparison of the structures revealed molecular rearrangements and interactions that mediate agonist recognition and early steps in signal transduction in α7 AChRs. The structures further revealed a ring of negative charge within the central vestibule, poised to contribute to cation selectivity. Structure-guided mutational studies disclosed distinctive contributions to agonist recognition and signal transduction in α7 AChRs. The structures provide a realistic template for structure-aided drug design and for defining structure–function relationships of α7 AChRs.

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Figure 1: Sequence and numbering of the α7–AChBP chimera and its alignment with related AChR sequences.
Figure 2: Overall structures of the α7–AChBP chimera and comparison to related structures.
Figure 3: Structures specific to α7 revealed by the α7–AChBP chimera.
Figure 4: Epibatidine-induced conformational changes.
Figure 5: Epibatidine-induced structural reorganization of the ligand-binding pocket and flanking regions.
Figure 6: Molecular recognition of epibatidine.
Figure 7: Pore-facing regions of inter-subunit contact.
Figure 8: Agonist binding after mutation of key residues.

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Acknowledgements

We thank Advanced Light Source Berkeley Center for Structural Biology staff members C. Ralston, P. Zwart, C. Bertoldo, A. Rozales and K. Royal for help with data collection, N. Chelyapov and University of Southern California NanoBiophysics Core Facility for help with multi-angle light scattering analyses and P. Taylor for providing cDNA encoding AChBP. This work is supported by US National Institutes of Health grants NS031744 to S.M.S. and HL076334 and GM064642 to L.C.

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Contributions

S.M.S. and L.C. supervised the project; S.H., N.B. and S.M.S. designed and built the α7–AChBP chimera; N.B. and S.H. expressed the protein; S.H., N.B. and S.-X.L. purified the protein; S.-X.L., S.H., C.D.D., K.N. and L.C. grew the crystals; S.-X.L. and L.C. collected diffraction data, solved and refined the structure; S.M.S. and N.B. conducted the radioligand binding experiments; and S.M.S., L.C., S.L. and S.H. wrote the paper.

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Correspondence to Steven M Sine or Lin Chen.

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The authors declare no competing financial interests.

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Supplementary Figures 1–11, Supplementary Tables 1 and 2 (PDF 1296 kb)

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Li, SX., Huang, S., Bren, N. et al. Ligand-binding domain of an α7-nicotinic receptor chimera and its complex with agonist. Nat Neurosci 14, 1253–1259 (2011). https://doi.org/10.1038/nn.2908

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