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

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Abstract
Proton NMR spectra at 300 MHz of neurotoxin III from venom of N. mossambica mossambica were reported. By 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 and .epsilon.-CH2 proton signals of some Lys residues were assigned to individual amino acid residues and their spatial microenvironment was determined. Results deduced on the solution structure of neurotoxin III agreed with the crystal structure of sea snake erabutoxins and with the previously established backbone folding and inter-residue interactions for N. naja oxiana short-chain neurotoxin in solution. The conformation of the .beta. turn in the 31-34 segment depended on the ionization state of the Asp-31 and His-32 side chain groups and an intricate electrostatic interaction existed 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 were related to an interaction mechanism of a neurotoxin molecule and a nicotinic acetylcholine receptor.