SPIN AND FLUORESCENCE LABELED NEUROTOXIN II. CONFORMATIONAL STUDIES AND INTERACTION OF THE TOXIN WITH THE ACETYLCHOLINE RECEPTOR

ABSTRACT Fifteen Naja naja oxiana neurotoxin II derivatives mono and di spin-labeled on Lys-15, Lys-25, Lys-26, Lys-44 and Lys-46 have been prepared and the position of the label(s) identified. Spin label distances to a number of the side chains were determined by 1 H NMR for the mono-labeled species and interlabel distances were determined by EPR for the di-labeled residues. Binding of the mono spin-labeled derivatives to solubilized acetylcholine receptor protein (AChR) from Torpedo marmorata was followed by EPR. By means of a spin probe technique, it was found that spin labels on Lys-15, Lys-25, Lys-46 and, especially Lys-26, are less accessible in the AChR complexes than in the free toxins. Involvement of the dansyl labels on Lys-26 and Lys-46 in the binding was demonstrated by fluorescence spectroscopy. The data obtained yielded evidence of a β-structure of the toxin and allowed preliminary characterization of the neurotoxin binding surface.