Acetylcholine interactions with tryptophan-184 of the α-subunit of the nicotinic acetylcholine receptor revealed by transferred nuclear Overhauser effect

Acetylcholine interactions with three genetically engineered fusion proteins containing peptides from the nicotinic acetylcholine receptor were studied by ID and 2D nuclear magnetic resonance methods. The three proteins were Torpedo α186-200, Torpedo α186-198, and human α183-204 of the acetylcholine receptor fused to the first 323 residues of the E. coli protein trpE. Nuclear Overhauser effect studies revealed interactions of bound acetylcholine with tryptophan-184 present in the Torpedo α184-200, and the human α183-204 sequences. These interactions are between the N(CH₃)_3⁺ and CH₃ groups of acetylcholine with the aromatic protons of tryptophan. The appearance of these cross-peaks indicates a distance of less than 5 A between tryptophan and the bound ligand; however, direct contact has yet to be proven.