Identification of a new component of the agonist binding site of the nicotinic alpha 7 homooligomeric receptor.
Tryptophan 54 of the alpha 7 neuronal nicotinic homooligomeric receptor is homologous to gamma-Trp-55 and delta-Trp-57 of non-alpha subunits of Torpedo receptor labeled by d-tubocurarine. This residue was mutated on the alpha 7-V201-5-hydroxytryptamine (5HT)3 homooligomeric chimera, which displays alpha 7 nicotinic pharmacology, and for which both equilibrium binding studies and electrophysiological recordings could be carried out in parallel. Replacement of Trp-54 by a Phe, Ala, or His causes a progressive decrease both in binding affinity and in responses (EC50 or IC50) for acetylcholine, nicotine, and dihydro-beta-erythroidine, without significant modification in alpha-Bgtx binding. Except for Gln-56, comparatively small effects are observed when the other residues of the 52-58 region are mutated into alanine. These data support the participation of Trp-54 to ligand binding, and provide evidence for a new "complementary component" of the alpha 7 nicotinic binding site, distinct from its three-loop "principal component," and homologous to the "non-alpha component" present on gamma and delta subunits.
Corringer
P J
PJ
Unité de recherche associée D1284, CNRS, Institut Pasteur, Paris, France.
Galzi
J L
JL
Eiselé
J L
JL
Bertrand
S
S
Changeux
J P
JP
Bertrand
D
D
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002038:Bungarotoxins / Q000378:metabolism; D002645:Chickens; D018076:DNA, Complementary / Q000235:genetics; D007700:Kinetics; D008969:Molecular Sequence Data; D009538:Nicotine / Q000378:metabolism; D018722:Nicotinic Agonists; D011485:Protein Binding; D051381:Rats; D011978:Receptors, Nicotinic / Q000737:chemistry*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014101:Torpedo / Q000378:metabolism
D002038:Bungarotoxins; D018076:DNA, Complementary; D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; D009538:Nicotine