Regions of beta 2 and beta 4 responsible for differences between the steady state dose-response relationships of the alpha 3 beta 2 and alpha 3 beta 4 neuronal nicotinic receptors.
We constructed chimeras of the rat beta 2 and beta 4 neuronal nicotinic subunits to locate the regions that contribute to differences between the acetylcholine (ACh) dose-response relationships of the alpha 3 beta 2 and alpha 3 beta 4 receptors. Expressed in Xenopus oocytes, the alpha 3 beta 2 receptor displays an EC50 for ACh approximately 20-fold less than the EC50 of the alpha 3 beta 4 receptor. The apparent Hill slope (n(app)) of alpha 3 beta 2 is near one whereas the alpha 3 beta 4 receptor displays an n(app) near two. Substitutions within the first 120 residues convert the EC50 for ACh from one wild-type value to the other. Exchanging just beta 2:104-120 for the corresponding region of beta 4 shifts the EC50 of ACh dose-response relationship in the expected direction but does not completely convert the EC50 of the dose-response relationship from one wild-type value to the other. However, substitutions in the beta 2:104-120 region do account for the relative sensitivity of the alpha 3 beta 2 receptor to cytisine, tetramethylammonium, and ACh. The expression of beta 4-like (strong) cooperativity requires an extensive region of beta 4 (beta 4:1-301). Relatively short beta 2 substitutions (beta 2:104-120) can reduce cooperativity to beta 2-like values. The results suggest that amino acids within the first 120 residues of beta 2 and the corresponding region of beta 4 contribute to an agonist binding site that bridges the alpha and beta subunits in neuronal nicotinic receptors.
Cohen
B N
BN
Division of Biomedical Sciences, University of California, Riverside 92521-0121, USA.
Figl
A
A
Quick
M W
MW
Labarca
C
C
Davidson
N
N
Lester
H A
HA
D000109:Acetylcholine / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018722:Nicotinic Agonists / Q000494:pharmacology*; D009865:Oocytes / Q000378:metabolism; D051381:Rats; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014981:Xenopus
D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; D011993:Recombinant Fusion Proteins; D000109:Acetylcholine