title: Ribosomal biosynthesis of the cyclic peptide toxins of Amanita mushrooms.
abstract: Some species of mushrooms in the genus Amanita are extremely poisonous and frequently fatal to mammals including humans and dogs. Their extreme toxicity is due to amatoxins such as alpha- and beta-amanitin. Amanita mushrooms also biosynthesize a chemically related group of toxins, the phallotoxins, such as phalloidin. The amatoxins and phallotoxins (collectively known as the Amanita toxins) are bicyclic octa- and heptapeptides, respectively. Both contain an unusual Trp-Cys crossbridge known as tryptathionine. We have shown that, in Amanita bisporigera, the amatoxins and phallotoxins are synthesized as proproteins on ribosomes and not by nonribosomal peptide synthetases. The proproteins are 34-35 amino acids in length and have no predicted signal peptides. The genes for alpha-amanitin (AMA1) and phallacidin (PHA1) are members of a large family of related genes, characterized by highly conserved amino acid sequences flanking a hypervariable "toxin" region. The toxin regions are flanked by invariant proline (Pro) residues. An enzyme that could cleave the proprotein of phalloidin was purified from the phalloidin-producing lawn mushroom Conocybe apala. The enzyme is a serine protease in the prolyl oligopeptidase (POP) subfamily. The same enzyme cuts at both Pro residues to release the linear hepta- or octapeptide.
authors.affiliation: Department of Energy Plant Research Laboratory, Michigan State University, E. Lansing, MI 48824, USA. walton@msu.edu
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Walton
authors.forename: Heather E
authors.initials: HE
authors.lastname: Hallen-Adams
authors.forename: Hong
authors.initials: H
authors.lastname: Luo
mesh_terms: D000363:Agaricales / Q000737:chemistry* / Q000201:enzymology; D000546:Amanitins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010456:Peptides, Cyclic / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D011042:Poisons / Q000737:chemistry / Q000378:metabolism*; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000378:metabolism
chemical_list: D000546:Amanitins; D010456:Peptides, Cyclic; D011042:Poisons; D011498:Protein Precursors