TY - JOUR
T1 - A peptide agonist acts by occupation of a monomeric G protein-coupled receptor
T2 - Dual sites of covalent attachment to domains near TM1 and TM7 of the same molecule make biologically significant domain-swapped dimerization unlikely
AU - Hadac, Elizabeth M.
AU - Ji, Zongshi
AU - Pinon, Delia I.
AU - Henne, Randal M.
AU - Lybrand, Terry P.
AU - Miller, Laurence J.
PY - 1999/6/17
Y1 - 1999/6/17
N2 - Membrane receptor dimerization is a well-established event for initiation of signaling at growth factor receptors and has been postulated to exist for G protein-coupled receptors, based on correction of nonfunctional truncated, mutant, or chimeric constructs by coexpression of appropriate normal complementary receptor domains. In this work, we have directly explored the molecular composition of the minimal functional unit of an agonist ligand and the wild-type G protein-coupled cholecystokinin (CCK) receptor, using photoaffinity labeling with a CCK analogue probe incorporating dual photolabile benzoylphenylalanine (Bpa) residues as sites of covalent attachment. This probe, 125I-D-Tyr-Gly-[(Nle28,31, Bpa29,33)CCK-26-33], was shown to represent a full agonist and to specifically label the CCK receptor. Like probes incorporating individual photolabile residues in these positions, the two Bpa residues in the dual photoprobe covalently labeled receptor domains in the amino-terminal tail outside TM1 and in the third extracellular loop outside TM7. Absence of demonstrable receptor dimerization after the establishment of dual sites of covalent attachment supports the presence of these two domains within a single receptor molecule. Demonstration of the covalent adduct of a single probe molecule with the two cyanogen bromide fragments of the CCK receptor representing the expected domains further supports this interpretation. Thus, while domain-swapped dimerization of G protein-coupled receptors may be possible as a mechanism of rescue for nonfunctional molecules, it is not necessary for ligand binding and initiation of signaling at a wild-type receptor in this superfamily. The functional unit for CCK action is normally a ligand-receptor monomer.
AB - Membrane receptor dimerization is a well-established event for initiation of signaling at growth factor receptors and has been postulated to exist for G protein-coupled receptors, based on correction of nonfunctional truncated, mutant, or chimeric constructs by coexpression of appropriate normal complementary receptor domains. In this work, we have directly explored the molecular composition of the minimal functional unit of an agonist ligand and the wild-type G protein-coupled cholecystokinin (CCK) receptor, using photoaffinity labeling with a CCK analogue probe incorporating dual photolabile benzoylphenylalanine (Bpa) residues as sites of covalent attachment. This probe, 125I-D-Tyr-Gly-[(Nle28,31, Bpa29,33)CCK-26-33], was shown to represent a full agonist and to specifically label the CCK receptor. Like probes incorporating individual photolabile residues in these positions, the two Bpa residues in the dual photoprobe covalently labeled receptor domains in the amino-terminal tail outside TM1 and in the third extracellular loop outside TM7. Absence of demonstrable receptor dimerization after the establishment of dual sites of covalent attachment supports the presence of these two domains within a single receptor molecule. Demonstration of the covalent adduct of a single probe molecule with the two cyanogen bromide fragments of the CCK receptor representing the expected domains further supports this interpretation. Thus, while domain-swapped dimerization of G protein-coupled receptors may be possible as a mechanism of rescue for nonfunctional molecules, it is not necessary for ligand binding and initiation of signaling at a wild-type receptor in this superfamily. The functional unit for CCK action is normally a ligand-receptor monomer.
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U2 - 10.1021/jm980732q
DO - 10.1021/jm980732q
M3 - Article
C2 - 10377216
AN - SCOPUS:0033578084
VL - 42
SP - 2105
EP - 2111
JO - Journal of Medicinal Chemistry
JF - Journal of Medicinal Chemistry
SN - 0022-2623
IS - 12
ER -