amatoxin

Amatoxins are a subgroup of at least nine related cyclic peptide toxins found in three genera of deadly poisonous mushrooms (Amanita, Galerina and Lepiota) and one species of the genus Pholiotina. Amatoxins are very potent, as little as half a mushroom cap can cause severe liver injury if swallowed.

== Structure == thumb|The backbone structure (black) is the same in all the amatoxins and five variable groups (red) determine the specific compound. The compounds have a similar structure, that of eight amino-acid residues arranged in a conserved macrobicyclic motif (an overall pentacyclic structure when counting the rings inherent in the proline and tryptophan-derived residues); they were isolated in 1941 by Heinrich O. Wieland and Rudolf Hallermayer. All amatoxins are cyclic peptides that are synthesized as 35-amino-acid proproteins, from which the final eight amino acids are cleaved by a prolyl oligopeptidase. The schematic amino acid sequence of amatoxins is Ile-Trp-Gly-Ile-Gly-Cys-Asn-Pro with cross-linking between Trp and Cys via the sulfoxide (S=O) moiety and hydroxylation in variants of the molecule; enzymes for these processing steps remain unknown.