Article

Antagonist binding profile of the split chimeric muscarinic m2-trunc/m3-tail receptor

Department of Neuroscience, University of Pisa, Italy.
European Journal of Pharmacology (Impact Factor: 2.68). 09/1998; 355(2-3):267-74. DOI: 10.1016/S0014-2999(98)00485-3
Source: PubMed

ABSTRACT Recent evidence suggests that G-protein-coupled receptors can behave as multiple subunit receptors, and can be split into parts, maintaining their binding ability. Transfection of a truncated muscarinic m2 receptor (containing transmembrane domains I-V, named m2-trunc) with a gene fragment coding for the carboxyl-terminal receptor portion of the muscarinic m3 receptor (containing transmembrane domains VI and VII, named m3-tail) results in the formation of a binding site with a high affinity for the muscarinic ligand N-[3H]methylscopolamine. In this paper we analyse the antagonist binding profile of this chimeric m2-trunc/m3-tail receptor in comparison with the wild-type muscarinic m2 and m3 receptors. While many of the substances tested had an intermediate affinity for the chimeric m2-trunc/m3-tail receptor compared with m2 and m3, some compounds were able to distinguish between the chimeric m2-trunc/m3-tail receptor on the one hand and the m2 or the m3 receptor on the other. Among them, tripitramine (a high-affinity M2 receptor antagonist) bound to the m2-trunc/m3-tail receptor with the same affinity as m2, but it bound to the m3 receptor with a 103-fold lower affinity; pirenzepine (a selective muscarinic M1 receptor antagonist) bound to the chimeric receptor with an affinity that was 12- and 3-fold higher than that of m2 and m3, respectively. The results of this study demonstrate that the chimeric m2-trunc/m3-tail receptor has a pharmacological profile distinct from that of the originating muscarinic m2 and m3 receptors.

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    • "Transmembrane helices I-V and VI-VII form essentially independent folding domains. GPCR sequences can be split between transmembrane helices V and VI, and, when these fragments are co-expressed, functional receptors can be reconstituted (Maggio et al., 1996; Barbier et al., 1998; Scarselli et al., 2000). Co-expression of a reciprocal chimaera containing transmembrane regions I-V of the α2C adrenoceptor and helices VI and VII of the muscarinic m3 acetylcholine receptor, or vice versa, results in the reconstitution of binding sites for ligands for both of the native receptors. "
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