Diversity of structure, signaling and regulation within the family of muscarinic cholinergic receptors.
Acetylcholine signals through two types of unrelated membrane receptors referred to as nicotinic (nAChR) and muscarinic (mAChR) acetylcholine receptors. Nicotinic acetylcholine receptors were the first neurotransmitter receptors to be purified, cloned, and sequenced, and much is known about these proteins. In contrast, until 5 years ago relatively little was known about the muscarinic receptors. Since then there has been an explosion of information concerning the structure, signaling, and regulation of what is now known to be a family of muscarinic receptors. This review discusses the five identified members of the mAChR family and their coupling to the multiple G proteins that allow mAChRs to modulate many different types of signal transduction pathways. The five members of this family that have been identified so far have striking homology in their hydrophobic membrane domains but possess distinct cytoplasmic domains between the fifth and sixth membrane-spanning regions. These cytoplasmic domains appear to contain important determinants for receptor/G protein interaction and are likely to contain phosphorylation sites that regulate these interactions. mAChR agonists have been shown to induce phosphorylation of mAChR in intact cells, and the evidence that suggests that receptor phosphorylation may play a role in the regulation of receptor function is discussed.
Hosey
M M
MM
Department of Pharmacology, Northwestern University Medical School, Chicago, Illinois 60611.
D000818:Animals; D002645:Chickens; D017868:Cyclic AMP-Dependent Protein Kinases; D019204:GTP-Binding Proteins / Q000502:physiology; D006801:Humans; D051379:Mice; D010766:Phosphorylation; D011493:Protein Kinase C / Q000502:physiology; D011494:Protein Kinases / Q000502:physiology; D011976:Receptors, Muscarinic / Q000502:physiology* / Q000648:ultrastructure; D011978:Receptors, Nicotinic / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D051552:beta-Adrenergic Receptor Kinases
D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D011494:Protein Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D051552:beta-Adrenergic Receptor Kinases; D019204:GTP-Binding Proteins