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J Biol Chem. 2016 Apr 22;291(17):8862-75. doi: 10.1074/jbc.M115.681726. Epub 2016 Jan 29.

An Antibody Biosensor Establishes the Activation of the M1 Muscarinic Acetylcholine Receptor during Learning and Memory.

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From the Medical Research Council Toxicology Unit and.
Eli Lilly and Co. Neuroscience, Erl Wood Manor, Windlesham, Surrey GU20 6PH, United Kingdom.
Protein and Nucleic Acid Chemistry Laboratory, University of Leicester, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, United Kingdom.
the Department of Molecular and Cell Biology, University of Leicester, Henry Wellcome Building, Lancaster Road, Leicester LE1 9HN, United Kingdom.
Eli Lilly and Co. Neuroscience, Lilly Corporate Center, Indianapolis, Indiana 46285, and.
From the Medical Research Council Toxicology Unit and


Establishing the in vivo activation status of G protein-coupled receptors would not only indicate physiological roles of G protein-coupled receptors but would also aid drug discovery by establishing drug/receptor engagement. Here, we develop a phospho-specific antibody-based biosensor to detect activation of the M1 muscarinic acetylcholine receptor (M1 mAChR) in vitro and in vivo Mass spectrometry phosphoproteomics identified 14 sites of phosphorylation on the M1 mAChR. Phospho-specific antibodies to four of these sites established that serine at position 228 (Ser(228)) on the M1 mAChR showed extremely low levels of basal phosphorylation that were significantly up-regulated by orthosteric agonist stimulation. In addition, the M1 mAChR-positive allosteric modulator, 1-(4-methoxybenzyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid, enhanced acetylcholine-mediated phosphorylation at Ser(228) These data supported the hypothesis that phosphorylation at Ser(228) was an indicator of M1 mAChR activation. This was further supported in vivo by the identification of phosphorylated Ser(228) on the M1 mAChR in the hippocampus of mice following administration of the muscarinic ligands xanomeline and 1-(4-methoxybenzyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid. Finally, Ser(228) phosphorylation was seen to increase in the CA1 region of the hippocampus following memory acquisition, a response that correlated closely with up-regulation of CA1 neuronal activity. Thus, determining the phosphorylation status of the M1 mAChR at Ser(228) not only provides a means of establishing receptor activation following drug treatment both in vitro and in vivo but also allows for the mapping of the activation status of the M1 mAChR in the hippocampus following memory acquisition thereby establishing a link between M1 mAChR activation and hippocampus-based memory and learning.


G protein-coupled receptor (GPCR); drug discovery; hippocampus; learning; mass spectrometry (MS); memory; phosphorylation

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