Conformation of the mushroom toxin beta-amanitin in the crystalline state.

A single crystal X-ray diffraction analysis of beta-amanitin, a bicyclic octapeptide toxin isolated from the poisonous mushroom Amanita phalloides, shows that the molecule has distinct regions of hydrophilic and hydrophobic residues and two 18-membered rings. The study confirms the proposed chemical sequence and the configuration of the residues. All eight peptide groups are in the trans conformation. Four intramolecular hydrogen bonds, two strong and two weak, occur in the structure. The toxin cocrystallizes with seven water and three ethanol molecules and participates in an extensive hydrogen-bonding network. The crystal structure was solved by direct methods. The space group is P2(1)2(1)2(1), and unit cell dimensions are a = 14.004(3), b = 14.943(3), and c = 30.794(7) A.