A single residue in the M2-M3 loop is a major determinant of coupling between binding and gating in neuronal nicotinic receptors.
Binding of agonists to nicotinic acetylcholine receptors generates a sequence of changes that activate a cation-selective conductance. By measuring electrophysiological responses in chimeric alpha7/alpha3 receptors expressed in Xenopus oocytes, we have showed the involvement of the M2-M3 loop in coupling agonist binding to the channel gate. An aspartate residue therein, Asp-266 in the alpha7 subunit, was identified by site-directed mutagenesis as crucial, since mutants at this position exhibited very poor functional responses to three different nicotinic agonists. We have extended this investigation to another neuronal nicotinic receptor (alpha3/beta4), and found that a homologous residue in the beta4 subunit, Asp-268, played a similar role in coupling. These findings are consistent with a hypothesis that the aspartate residue in the M2-M3 loop, which is conserved in all homomer-forming alpha-type subunits and all neuronal beta-type subunits that combine to form functional receptors, is a major determinant of information transmission from binding site to channel gate in all neuronal nicotinic receptors.
Campos-Caro
A
A
Departamento de Neuroquímica, Universidad de Alicante, Spain.
Sala
S
S
Ballesta
J J
JJ
Vicente-Agulló
F
F
Criado
M
M
Sala
F
F
D000595:Amino Acid Sequence; D000818:Animals; D015640:Ion Channel Gating; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009474:Neurons / Q000378:metabolism*; D018722:Nicotinic Agonists / Q000494:pharmacology; D017354:Point Mutation; D011485:Protein Binding; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014981:Xenopus
D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic