Spatial Relationships between Drug Binding Sites on the Surface of the Acetylcholine Receptor: Preparation and Interaction of Fluorescent Alpha-Toxins and Decidium with the Acetylcholine Receptor

摘要

This report described the development of fluorescent probes of the nicotinic acetylcholine receptor and their use in an analysis of drug and a-toxin interaction with the acetylcholine receptor. Section I develops a new theoretical framework is utilized in an analysis of the interaction of fluorescein isothiocyanates toxin with the acetylcholine receptor. We show that when alpha-toxin binds to the receptor, the region around the alpha-toxin's lysine 23 is completely accessible to the solute. As more site-specifically labeled toxins are prepared, it will be possible to obtain clearer picture of the disposition of the alpha-toxin molecule on the surface of the receptor. Section II summarizes the characterization of the interaction of a novel decamethonium homolog, decidium, with the acetylcholine receptor. Decidium is shown to bind to both the agonist/antagonist and noncompetitive blocking binding sites on the surface of the receptor and displays specific spectral shifts associated with the interaction with each class of drug binding site. Fluorescence energy transfer studies between decidium and FITC-toxin indicate some proximity of the alpha-toxin binding sites and the lipid bilayer. Section III summarizes our progress in site-specifically labeling alpha-toxin with FITC, erythrosin isothiocyanate (EITC), and tetramethylrhodamine isothiocyanate (TRITC). Utilizing new high resolution isoelectric focusing techniques, it should be possible to isolate semipreparative quantities of site-specifically-labeled alpha-toxins.