A proton NMR study at 500 MHz of leiurotoxin I in water is presented. Nearly complete sequence-specific assignments of the individual backbone and side-chain proton resonances were achieved using through-bond and through-space connectivities obtained from standard two-dimensional NMR techniques. The secondary structure of this toxin is inferred from a combination of short-range nuclear Overhauser enhancements, scalar couplings and proton/deuteron exchange rates. Three disulflde bridges locate the N-terminal part (that is α-helical from residue 6 to 16) on one side of a C-terminal two stranded antiparallel β sheet (from Leu18 to Val29). The latter features a tight turn at Gly23-Asp24.
