Stopped-flow fluorescence studies on binding of snake neurotoxins to acetylcholine receptor

The stopped-flow technique has been applied to observe the time dependence of a tryptophanyl fluorescence change upon binding of postsynaptic snake neurotoxins to nicotinic acetylcholine receptor (Narke japonica). Examination of the kinetics of the fluorescence change reflecting a conformational change in the receptor in the process of binding of 28 short neurotoxins and 8 long neurotoxins to the receptor has revealed the following. Short neurotoxins associate with the receptor more rapidly than do long neurotoxins. A positive charge on the side chains of residues 27 and 30 and the overall net charge of the toxin molecule governs the magnitude of the binding rates of toxins to the receptor. The invariant residue Asp-31 is important for neurotoxicity, but is not critical for binding ability with the receptor.This article was presented during the proceedings of the International Conference on Macromolecular Structure and Function, held at the National Defence Medical College, Tokorozawa, Japan, December 1985.