Antagonist binding profile of the split chimeric muscarinic m2-trunc/m3-tail receptor.
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.
Department of Neuroscience, University of Pisa, Italy.
P
P
Barbier
A
A
Colelli
M L
ML
Bolognesi
A
A
Minarini
V
V
Tumiatti
G U
GU
Corsini
C
C
Melchiorre
R
R
Maggio
D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D008969:Molecular Sequence Data; D018727:Muscarinic Antagonists / Q000378:metabolism*; D051381:Rats; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
D018727:Muscarinic Antagonists; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; D011993:Recombinant Fusion Proteins