Conotoxin MI inhibits the alpha-delta acetylcholine binding site of the Torpedo marmorata receptor.

The muscle-type nicotinic receptor has two pharmacologically distinguishable acetylcholine binding sites at the alpha-gamma and alpha-delta subunit interfaces; alpha-conotoxins can bind them selectively. As reported, alpha-conotoxin MI has greater affinity for the site near the alpha-delta interface of the BC(3)H1 cell receptor but, in the case of the Torpedo californica receptor, displays greater affinity for that near the alpha-gamma interface. To further investigate ligand selectivity, we study the conotoxin MI-Torpedo marmorata receptor interaction.