NMR-SPECTRA AND RESTRAINED MOLECULAR-DYNAMICS OF THE MUSHROOM TOXIN VIROISIN

The conformation of viroisin, the monocyclic toxic heptapeptide of the virotoxin family from mushroom Amanita virosa, was analysed using two -dimensional nuclear magnetic resonance spectroscopy and restrained mo lecular dynamics simulations. All proton signals were completely assig ned, and interproton distances were determined using data from rotatin g-frame nuclear Overhauser enhancement. The backbone dihedral angles w ere deduced from measurements of coupling constants. The temperature d ependence of the amide proton chemical shifts provided information abo ut hydrogen bonding. Six probable solution conformations of viroisin w ere derived from the use of distance geometry and restrained molecular dynamics based on a set of distance constraints obtained from experim ental data. The results of the structural analysis indicate that viroi sin has a well ordered conformation in solution. In all these conforma tions the functional groups essential for toxicity orient themselves i n the same direction so as to bind to the target proteins. This featur e is consistent with previous results about the formation of a hydroph obic pocket on one side of the molecule. (C) Munksgaard 1994.