Intramolecular interactions in muscarinic acetylcholine receptors studied with chimeric m2/m5 receptors

Z Pittel and J Wess

National Institute of Diabetes and Digestive and Kidney Diseases, Laboratory of Bioorganic Chemistry, Bethesda, Maryland 20892.

Current models of the three-dimensional structures of muscarinic acetylcholine receptors and other G protein-coupled receptors are based primarily on high-resolution electron diffraction data obtained with bacteriorhodopsin, the molecular structure of which is characterized by the presence of seven alpha-helical transmembrane domains (TM I-VII). However, bacteriorhodopsin does not couple to G proteins and its primary sequence lacks a series of amino acids that are conserved among virtually all G protein-coupled receptors. Therefore, it remains to be shown experimentally whether the molecular structures of these functionally different proteins are in fact identical. To address this question, we have analyzed the pharmacological properties of a series of hybrid human m2/m5 muscarinic receptors. Initially, we identified several chimeric constructs that, upon transient expression in COS-7 cells, were unable to bind significant amounts of the muscarinic antagonists N-[3H]methylscopolamine and [3H]quinuclidinyl benzilate. A common structural feature of these constructs was the presence of m2 receptor sequence in TM VII and of m5 receptor sequence in TM I. The ligand-binding activity of these "pharmacologically inactive" hybrid receptors could be restored by replacing TM I (consisting of m5 receptor sequence) with the corresponding m2 receptor domain. These data provide the first direct experimental evidence that the molecular architecture of muscarinic receptors (and, most likely, that of other G protein-coupled receptors) resembles that of bacteriorhodopsin, in that the seven TM helices are arranged in a ring-like fashion such that TM I lies directly adjacent to TM VII.

Volume 45, Issue 1, pp. 61-64, 01/01/1994
Copyright © 1994 by American Society for Pharmacology and Experimental Therapeutics

This article has been cited by other articles:

				D. Yin, S. Gavi, H.-y. Wang, and C. C. Malbon Probing Receptor Structure/Function with Chimeric G-Protein-Coupled Receptors Mol. Pharmacol., June 1, 2004; 65(6): 1323 - 1332. [Abstract] [Full Text] [PDF]

				U. Gether Uncovering Molecular Mechanisms Involved in Activation of G Protein-Coupled Receptors Endocr. Rev., February 1, 2000; 21(1): 90 - 113. [Abstract] [Full Text]

				U. Gether and B. K. Kobilka G Protein-coupled Receptors. II. MECHANISM OF AGONIST ACTIVATION J. Biol. Chem., July 17, 1998; 273(29): 17979 - 17982. [Full Text] [PDF]

				S. D. Feighner, A. D. Howard, K. Prendergast, O. C. Palyha, D. L. Hreniuk, R. Nargund, D. Underwood, J. R. Tata, D. C. Dean, C. P. Tan, et al. Structural Requirements for the Activation of the Human Growth Hormone Secretagogue Receptor by Peptide and Nonpeptide Secretagogues Mol. Endocrinol., January 1, 1998; 12(1): 137 - 145. [Abstract] [Full Text]

				L. B. Kozell and K. A. Neve Constitutive Activity of a Chimeric D2/D1 Dopamine Receptor Mol. Pharmacol., December 1, 1997; 52(6): 1137 - 1149. [Abstract] [Full Text]

				D. Shire, B. Calandra, M. Delpech, X. Dumont, M. Kaghad, Gér. Le Fur, D. Caput, and P. Ferrara Structural Features of the Central Cannabinoid CB1 Receptor Involved in the Binding of the Specific CB1 Antagonist SR 141716A J. Biol. Chem., March 22, 1996; 271(12): 6941 - 6946. [Abstract] [Full Text] [PDF]

				J. Liu, T. Schöneberg, M. van Rhee, and Jür. Wess Mutational Analysis of the Relative Orientation of Transmembrane Helices I and VII in G Protein-coupled Receptors J. Biol. Chem., August 18, 1995; 270(33): 19532 - 19539. [Abstract] [Full Text] [PDF]