2AMK:
reference: Random mutagenesis of the M3 muscarinic acetylcholine receptor expressed in yeast: identification of second-site mutations that restore function to a coupling-deficient mutant M3 receptor., Li B, Nowak NM, Kim SK, Jacobson KA, Bagheri A, Schmidt C, Wess J, J Biol Chem. 2005 Feb 18;280(7):5664-75. Epub 2004 Nov 30. PMID: 15572356

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