THE DISULFIDE BRIDGES OF TOXIN-2 FROM THE SCORPION CENTRUROIDES-NOXIUS HOFFMANN AND ITS 3-DIMENSIONAL STRUCTURE CALCULATED USING THE COORDINATES OF VARIANT-3 FROM CENTRUROIDES-SCULPTURATUS

The disulfide bridges of toxin 2 from the venom of the scorpion Centru roides noxius Hoffmann were found by amino acid sequence determination of fragments of native toxin, produced by enzymatic cleavage and sepa rated by high-performance liquid chromatography (HPLC). They are: Cys( 12)-Cys(65), CyS(16)-CyS(41),CyS(25)-CyS(46) and Cys(29)-Cys(48). The coordinates of the X-ray diffraction structure of toxin variant 3 of C . sculpturatus [(1980) Proc. Natl. Acad. Sci. USA 77, 6496-6500] were used to construct a three-dimensional model of toxin 2. All the amino acid replacements were easily accommodated, and the modeled structure reveals a clustered pattern of sequence variation, which may help to i dentify residues responsible for functional differences among toxins o f mammals and insects.