CARDIOTOXIN-V4II FROM NAJA-MOSSAMBICA-MOSSAMBICA - THE REFINED CRYSTAL-STRUCTURE

The crystal structure of cardiotoxinV4II fromNaja mossambica mossambica was refined to 2.5A °resolution. Fifty ordered solvent sites were localized and included in the refinement. The finalR factor is 0.197 (λ(2sinθ) < 5A °; F > 3σ). The three-dimensional structure is characterized by two β-sheets. Of particular interest is the two-stranded β-sheet in the N-terminal region. This shows a large right-handed twist and, though strongly connected to the core of the molecule, and in particular to the C-terminal end, protrudes out of the bulk of the molecule. The segment of four amino acid residues connecting the two strands of this sheet is particularly exposed. It contains an invariant proline residue that has probably an important structural role, and is completely hydrophobic. Two other conserved hydrophobic zones were identified; the largest extends over the second and third loops, on one side only of the molecule. All side-chains of invariant hydrophobic character (except proline residues) belong to one of these three zones. Also discussed are the dimeric assembly and the rather loose packing in the crystal. The three-dimensional structure is compared with that of short and long α-neurotoxins. Comparison with two-dimensional nuclear magnetic resonance results on the 68% homologous cardiotoxinCTXIIb shows an excellent overall agreement. A few differences are probably genuine. © 1990 Academic Press Limited.