TY - JOUR T1 - Helix 8 of the M<sub>1</sub> Muscarinic Acetylcholine Receptor: Scanning Mutagenesis Delineates a G Protein Recognition Site. JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.110.070177 SP - mol.110.070177 AU - Robert G. Kaye AU - Jose W. Saldanha AU - Zhi-Liang Lu AU - Edward C. Hulme Y1 - 2011/01/01 UR - http://molpharm.aspetjournals.org/content/early/2011/01/19/mol.110.070177.abstract N2 - We have used alanine-scanning mutagenesis followed by functional expression and molecular modelling to analyse the role of the 14 residues Asn422-Cys435 C-terminal to trans-membrane (TM) helix 7 of the M1 muscarinic acetylcholine receptor. The results suggest that they form an 8th (H8) helix, associated with the cytoplasmic surface of the cell membrane in the active state of the receptor. We suggest that the amide side-chain of Asn422 may act as a cap to the C-terminus of TM7 stabilising its junction with H8, while the side-chain of Phe429 may restrict relative movements of H8 and the C-terminus of TM7 in the inactive ground state of the receptor. We have identified four residues, Phe425, Arg426, Thr428 and Leu432, which are important for G protein binding and signalling. These may form a docking site for the C-terminal helix of the G protein, and collaborate with G protein recognition residues elsewhere in the cytoplasmic domain of the receptor to form a coherent surface for G protein binding in the activated state of the receptor. ER -