A 1H nuclear-magnetic-resonance study of the solution conformation of the isoinhibitor K from Helix pomatia.

The isoinhibitor K from Helix pomatia was investigated by high-resolution 1H nuclear magnetic resonance at 360 MHZ. Detailed studies of the labile protons and the resonances of the aromatic residues indicated extensive homologies between the spatial structures of the snail inhibitor, the basic pancreatic trypsin inhibitor (Kunitz) from bovine tissue and the cos colostrum trypsin inhibitor. Comparison of these three homologous inhibitors indicated that the overall flexibility of the globular protein conformation is reduced and its stability with respect to thermal denaturation raised when the content of amino acids with charged side chains is increased. It is suggested that this relation between amino acid composition and stability of the globular solution structure might be valid also for other classes of homologous proteins.