[Secondary structure and assignment of signals in two-dimensional 1H-NMR spectra of the Buthus eupeus neurotoxin I5A].

The complete assignment of the 500 MHz 1H nuclear magnetic resonance spectrum of the insectotoxin I5A isolated from Buthus eupeus scorpion venom is performed by two-dimensional spectroscopy. The analysis of nuclear Overhauser effects for the protons of neighbouring residues in the amino acid sequence established the secondary structure of the molecule: alpha-helical part from Asn11 to Gly21 and anti-parallel beta-structure from asn23 to Asn34 with the beta-turn Phe27-Gly28-Pro29-Gln30. Three X-Pro peptide bonds have trans configuration. The primary structure of isotoxin was corrected by NMR and confirmed by sequencing.