Role of Key Aromatic Residues in the Ligand-binding Domain of α7 Nicotinic Receptors in the Agonist Action of β-Amyloid

Soluble beta-amyloid (A beta) resides in certain regions of the brain at or near picomolar concentration, rising in level during the prodromic stage of Alzheimer disease. Recently, we identified the homomeric alpha 7 nicotinic acetylcholine receptor (alpha 7-nAChR) as one possible functional target for picomolar A beta. This study was aimed at addressing which residues in alpha 7-nAChRs potentially interact with A beta to regulate the presynaptic function of this receptor. Site-directed mutagenesis was carried out to study the key aromatic residues in the mouse alpha 7-nAChR agonist-binding pocket. Mutations of tyrosine188 resulted in a decrease in activation of presynaptic alpha 7-nAChRs by ACh and A beta but with no change in response to nicotine, indicating the critical role of Tyr-188 in presynaptic regulation by A beta. Coimmunoprecipitation additionally revealed direct binding of A beta to alpha 7-nAChRs and to the Tyr-188 mutant receptor. In contrast, mutations of Tyr-195 in alpha 7-nAChR led to decreased activation by nicotine without apparent effects on ACh- or A beta-induced responses. Agonist-induced responses of Tyr-93 mutant alpha 7-nAChRs indicated possible interactions of nicotine and A beta with its hydroxyl group, but there was no change in presynaptic responses after mutation of Trp-149. All of the mutants were shown to be expressed on the plasma membrane using cell surface labeling. Together, these results directly demonstrate an essential role for the aromatic residue Tyr-188 as a key component in the agonist binding domain for the activation of alpha 7-nAChRs by A beta