GPCRs (G-protein-coupled receptors) such as the M1 muscarinic receptor have so far proved recalcitrant to direct structure determination. Nevertheless systematic mutagenesis, particularly alanine scanning, has advanced our understanding of their structure–function relationships. GPCRs exhibit multiple conformational states with different affinities for and abilities to activate their cognate G-proteins. Ligand binding alters these conformational equilibria, thus promoting or inhibiting signalling. Alanine-scanning mutagenesis probes the relative contributions of a particular amino acid side chain to the stability of the ground and activated states of the receptor and its complexes. These determine the phenotype of the mutant receptor. Classification of the phenotypes suggests functional roles for particular amino acid side chains, allowing us to group them accordingly. From a rhodopsin-based homology model of the M1 mAChR, a coherent view emerges of how these clusters of residues function in ligand anchoring, transduction of binding energy, global structural stabilization and selective stabilization of the ground state or the activated state of the receptor. We can identify differences in ligand-binding modes, and suggest inter- and intra-molecular interactions that are weakened or broken, or formed or intensified during acetylcholine-induced activation. In due course, we may be able to extend these insights to activation by unconventional agonists.
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August 2007
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Conference Article|
July 20 2007
Phenotypic classification of mutants: a tool for understanding ligand binding and activation of muscarinic acetylcholine receptors
E.C. Hulme;
E.C. Hulme
1
1Division of Physical Biochemistry, MRC National Institute for Medical Research, Mill Hill, London NW7 1AA, U.K.
1To whom correspondence should be addressed (email ehulme@nimr.mrc.ac.uk).
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M.S. Bee;
M.S. Bee
1Division of Physical Biochemistry, MRC National Institute for Medical Research, Mill Hill, London NW7 1AA, U.K.
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J.A. Goodwin
J.A. Goodwin
1Division of Physical Biochemistry, MRC National Institute for Medical Research, Mill Hill, London NW7 1AA, U.K.
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Publisher: Portland Press Ltd
Received:
March 23 2007
Online ISSN: 1470-8752
Print ISSN: 0300-5127
© The Authors Journal compilation © 2007 Biochemical Society
2007
Biochem Soc Trans (2007) 35 (4): 742–745.
Article history
Received:
March 23 2007
Citation
E.C. Hulme, M.S. Bee, J.A. Goodwin; Phenotypic classification of mutants: a tool for understanding ligand binding and activation of muscarinic acetylcholine receptors. Biochem Soc Trans 1 August 2007; 35 (4): 742–745. doi: https://doi.org/10.1042/BST0350742
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