Differential Contribution of Subunit Interfaces to α9α10 Nicotinic Acetylcholine Receptor Function

Area of Science:

• Neuroscience
• Molecular Biology
• Pharmacology

Background:

• Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels assembled from various subunit combinations.
• Neuronal nAChRs typically comprise α and β subunits, forming heteromeric receptors with distinct binding sites.
• The α9α10 nAChR is an atypical heteromeric receptor composed solely of α subunits, with α9 forming homomeric receptors but α10 not forming functional homomeric channels.

Purpose of the Study:

• To investigate the distinct contributions of α9 and α10 subunits to the acetylcholine binding site in the α9α10 nAChR.
• To elucidate the structural and functional roles of subunit interfaces in α9α10 nAChR pharmacology.
• To understand the evolutionary basis for subunit asymmetry in mammalian α9α10 nAChRs.

Main Methods:

• Site-directed mutagenesis was employed to alter specific amino acid residues in α9 and α10 subunits.
• Electrophysiological recordings were used to assess receptor function and channel activity.
• Radioligand binding studies were performed to characterize ligand interactions with the receptors.

Main Results:

• Mutational analysis revealed that both α9 and α10 subunits contribute equally to the principal components of the α9α10 nAChR ligand-binding site.
• A W55T mutation in the α9 subunit impaired receptor binding and function, whereas the same mutation in the α10 subunit had no significant effect.
• These findings indicate a nonequivalent contribution of α9 and α10 subunits to the complementary components of the ligand-binding site.

Conclusions:

• The α9α10 nAChR exhibits an asymmetric ligand-binding site, with distinct roles for α9 and α10 subunits in binding site composition.
• This asymmetry arises from adaptive evolutionary changes in the mammalian α10 subunit, influencing its interaction with the binding site.
• Molecular docking studies support the observed asymmetry, highlighting the evolutionary divergence of subunit contributions to nAChR function.