Erabutoxin b. Initial protein refinement and sequence analysis at 0.140-nm resolution.

The crystal structure of the protein postsynaptic neurotoxin, erabutoxin b, has been refined at 0.140-nm resolution (R = 0.22) by restrained least-squares and interactive computer graphics. The study has established complete structural identity of the two sea-snake venom toxins, erabutoxin b and neurotoxin b, isolated from Laticauda semifasciata snakes taken in different Pacific Ocean waters. Two chemical-sequence inversion errors in erabutoxin b have been discovered during refinement, corrected and subsequently confirmed in both erabutoxin b and erabutoxin a by chemical analysis. The correct sequences are His6-Gln7, hitherto unsuspected, and Ser18-Pro19. The sequence correction His6-Gln7 explains the anomalous results of 1H NMR solution studies and those of early chemical modification experiments, which were in conflict with the previously published three-dimensional structure of erabutoxin b. On refinement, the five-stranded beta sheet described earlier is now shown to be discontinuous, split into a two-stranded beta loop and a three-stranded beta sheet. Unique features of the Pro44-Gly49 peripheral segment have now been identified. 51 water molecule positions have been located.