The three-dimensional structure of erabutoxin b, a short-chain neurotoxic 
peptide purified from the venom of the sea snake Laticauda semifasciata, was 
determined in aqueous solution by two-dimensional proton nuclear magnetic 
resonance and simulated annealing-based calculations. On the basis of 883 
assigned nuclear Overhauser effect (NOE) connectivities, 676 final distance 
constraints were derived and used together with 38 torsion angle (phi, chi 1) 
constraints, four distance constraints derived from disulfide bridges and 30 
distance constraints derived from hydrogen bonds. A total of 14 converged 
structures were obtained from 50 runs of calculations. The atomic 
root-mean-square difference about the mean coordinate positions (excluding the 
residues 18 to 22) is 0.60 A for backbone atoms (N, C alpha and C'). The protein 
consists of a core region from which three finger-like loops emerge outwards. It 
includes a short, two-stranded antiparallel beta-sheet of residues 2 to 5 and 13 
to 16, a three-stranded antiparallel beta-sheet involving residues 23 to 30, 35 
to 41 and 50 to 56, and four disulfide bridges in the core region. Comparison 
with two crystal structures of erabutoxin b at 1.4 A and 1.7 A resolution 
indicated that the solution and the crystal structures were very similar, but 
less defined regions were observed at the localized region of the tip of the 
central loop and the outside of the third loop in solution. Other short-chain 
alpha-neurotoxins showed structural characteristics similar to those of 
erabutoxin b.