M1 Muscarine성 수용체에서 123Arginine 잔기의 Site--mutagenesis가 신호전달계에 미치는 영향

Effects of Site-mutagenesisof 123Arginine residue in M1 Muscarinic Receptor on the Signal Transduction System

An exceptionally conserved sequence that is shared among most G protein-coupled neurotransmitter receptors is an aspartate-arginine-tyrosine triplet that is located at the second cytoplasmic domain. Using the m1 subtype of muscarinic acetylcholine receptors as an example, a point mutation of the arginine residue at position 123 into asparagine was induced. This mutation resulted in a complete blockade of the carbachol-induced increases of PI hydrolysis and intracellular Ca2+ level, in spite of the expression of the wild-type and mutant receptors at similar concentrations in Chinese hamster ovary cells. In marked contrast, the muscarinic agonist carbachol induced concentration-dependent enhancement of the activity of NO synthase at mutant m1 receptors although the enhancement was significantly smaller than at wild-type m1 receptors. These data suggest that this highly conserved arginine residue plays an important role in coupling of muscarinic receptors to the second messenger systems and the presence of alternate mechanisms of activation of neuronal NO synthase which might be operative in the absence of large changes in the concentration of cellular Ca2+.