Distinct sequence elements control the specificity of G protein activation by muscarinic acetylcholine receptor subtypes.
Relatively little is understood concerning the mechanisms by which subtypes of receptors, G proteins and effector enzymes interact to transduce specific signals. Through expression of normal, hybrid and deletion mutant receptors in Xenopus oocytes, we determined the G protein coupling characteristics of the functionally distinct m2 and m3 muscarinic acetylcholine receptor (mAChR) subtypes and identified the critical receptor sequences responsible for G protein specificity. Activation of a pertussis toxin insensitive G protein pathway, leading to a rapid and transient release of intracellular Ca2+ characteristic of the m3 receptor, could be specified by the transfer of as few as nine amino acids from the m3 to the m2 receptor. In a reciprocal manner, transfer of no more than 21 residues from the m2 to the m3 receptor was sufficient to specify activation of a pertussis toxin sensitive G protein coupled to a slow and oscillatory Ca2+ release pathway typical of the m2 subtype. Notably, these critical residues occur within the same region of the third cytoplasmic domain of functionally distinct mAChR subtypes.
Lechleiter
J
J
Department of Pharmacology, Mayo Foundation, Rochester, MN 55905.
Hellmiss
R
R
Duerson
K
K
Ennulat
D
D
David
N
N
Clapham
D
D
Peralta
E
E
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D003001:Cloning, Molecular; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D037342:Pertussis Toxin; D011950:Receptors, Cholinergic / Q000187:drug effects / Q000235:genetics* / Q000494:pharmacology; D011994:Recombinant Proteins / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014981:Xenopus
D011950:Receptors, Cholinergic; D011994:Recombinant Proteins; D010566:Virulence Factors, Bordetella; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins