TY - JOUR
T1 - The role of the aspartate-arginine-tyrosine triad in the m1 muscarinic receptor
T2 - Mutations of aspartate 122 and tyrosine 124 decrease receptor expression but do not abolish signaling
AU - Lu, Zhi Liang
AU - Curtis, Carol A.
AU - Jones, Philip G.
AU - Pavia, Jose
AU - Hulme, Edward C.
PY - 1997/2
Y1 - 1997/2
N2 - An Asp-Arg-Tyr triad occurs in a majority of rhodopsin-like G protein coupled receptors. The fully conserved Arg is critical for G protein activation, but the function of the flanking residues is not well understood. We expressed in COS-7 cells m1 muscarinic receptors that were mutated at Asp122 and Tyr124. Most mutations at either position strongly attenuated or prevented the expression of binding sites for the antagonist [3H]N- methylscopolamine. However, sites that were expressed displayed unaltered affinity for the antagonist. Receptor protein, visualized with a carboxyl- terminally directed antibody, was reduced but never completely abolished. The effects of these mutations were partially reversed by the deletion of 129 amino acids from the third intracellular loop of the receptor. In several cases, comparison of immunocytochemistry with binding measurements suggested the presence of substantial amounts of inactive, presumably misfolded, receptor protein. Some of the variants that bound [3H]N-methylscopolamine underwent small changes in their affinities for acetylcholine. All retained nearly normal abilities to mediate an acetylcholine-induced phosphoinositide response. We propose that Asp122 and Tyr124 make intramolecular contacts whose integrity is important for efficient receptor folding but that they do not participate directly in signaling. The role of these residues is completely distinct from that of Arg123, whose mutation abolishes signaling without diminishing receptor expression.
AB - An Asp-Arg-Tyr triad occurs in a majority of rhodopsin-like G protein coupled receptors. The fully conserved Arg is critical for G protein activation, but the function of the flanking residues is not well understood. We expressed in COS-7 cells m1 muscarinic receptors that were mutated at Asp122 and Tyr124. Most mutations at either position strongly attenuated or prevented the expression of binding sites for the antagonist [3H]N- methylscopolamine. However, sites that were expressed displayed unaltered affinity for the antagonist. Receptor protein, visualized with a carboxyl- terminally directed antibody, was reduced but never completely abolished. The effects of these mutations were partially reversed by the deletion of 129 amino acids from the third intracellular loop of the receptor. In several cases, comparison of immunocytochemistry with binding measurements suggested the presence of substantial amounts of inactive, presumably misfolded, receptor protein. Some of the variants that bound [3H]N-methylscopolamine underwent small changes in their affinities for acetylcholine. All retained nearly normal abilities to mediate an acetylcholine-induced phosphoinositide response. We propose that Asp122 and Tyr124 make intramolecular contacts whose integrity is important for efficient receptor folding but that they do not participate directly in signaling. The role of these residues is completely distinct from that of Arg123, whose mutation abolishes signaling without diminishing receptor expression.
UR - http://www.scopus.com/inward/record.url?scp=0031037632&partnerID=8YFLogxK
U2 - 10.1124/mol.51.2.234
DO - 10.1124/mol.51.2.234
M3 - Article
C2 - 9203628
AN - SCOPUS:0031037632
SN - 0026-895X
VL - 51
SP - 234
EP - 241
JO - Molecular Pharmacology
JF - Molecular Pharmacology
IS - 2
ER -