DETERMINATION OF THE 3-DIMENSIONAL SOLUTION STRUCTURE OF SCYLLATOXIN BY H-1 NUCLEAR-MAGNETIC-RESONANCE

The three-dimensional solution structure of Scyllatoxin (leiurotoxin I ) a venom peptide from the scorpion Leiurus quinquestriatus hebraeus w as determined at 1 Angstrom resolution by homonuclear proton n.m.r. me thods at 500 MHz. Data analysis and structure calculation followed con ventional protocols inherent to DIANA and related programs with two ex ceptions. First, distance constraints were obtained from two-dimension al nuclear Overhauser spectra by a previously described partial relaxa tion matrix approach. Second, since the pairing pattern of the six cys teine residues was not established a priori, the unequivocal assignmen t of the disulfide bridges was achieved exclusively from the n.m.r. da ta by a statistical analysis of preliminary DIANA structures. In the f inal calculation we used 227 upper distance constraints, 67 torsional constraints from vicinal coupling constants and ten stereospecific ass ignments of beta-methylene protons. Scyllatoxin folds into a compact e llipsoidal shape. An alpha-helix (defined with 0.24 Angstrom resolutio n) spanning 2.5 turns from Leu5 till Serl4 is stabilized by Cys8-Cys26 and Cys12-Cys28 disulfide bridges to the carboxy-terminal strand of a n antiparallel beta-sheet. The antiparallel beta-sheet (defined at 0.6 6 Angstrom resolution) extends from Leu18 to Val29 with a tight turn a t Gly23-Asp24 and displays a right-handed twist. Scyllatoxin competes with the toxins apamin from Apis mellifera mellifera and P05 from Andr octonus mauretanicus mauretanicus for the same or similar high conduct ance calcium-activated potassium channels. Consideration of presently known biological activities and three-dimensional structures of these toxins suggest a different toxin-receptor interaction of scyllatoxin a s compared to apamin and P05. (C) 1995 Academic Press Limited