The 1 H Nuclear‐Magnetic‐Resonance Spectra and Spatial Structure of the Naja mossambica mossambica Neurotoxin III

The proton NMR spectra at 300 MHz of neurotoxin III from venom of Naja mossambica mossambica are reported. By the use of double resonance techniques, pH dependence chemical shifts, isotope labeling technique, and comparison with homologous neurotoxins all proton signals in the aromatic and methyl regions as well as ɛ‐CH 2 proton signals of some lysine residues have been assigned to individual amino acid residues and their spatial microenvironment has been determined. The results deduced on the solution structure of neurotoxin III are in complete agreement with the crystal structure of sea snake erabutoxins as well as with the previously established backbone folding and inter‐residue interactions for the Naja naja oxiana short‐chain neurotoxin in solution. In addition evidence has been obtained (a) that the conformation of the β turn in the 31–34 segment depends on the ionization state of the Asp‐31 and His‐32 side chain groups and (b) that an intricate electrostatic interaction exists in a system of ionogenic groups of the invariant Lys‐27, Lys‐47, Asp‐31, Arg‐33, Glu‐38 and His‐32 residues. These aspects of dynamic conformation are related to an interaction mechanism of a neurotoxin molecule and a nicotinic acetylcholine receptor.