Search

Background: The cyclic peptide toxins of Amanita mushrooms, such as α-amanitin and phalloidin, are encoded by the "MSDIN" gene family and ribosomally biosynthesized. Based on partial genome sequence and PCR analysis, some members of the MSDIN family were previously identified in Amanita bisporigera, and several other members are known from other species of Amanita. However, the complete complement in any one species, and hence the genetic capacity for these fungi to make cyclic peptides, remains unknown. Results: Draft genome sequences of two cyclic peptide-producing mushrooms, the "Death Cap" A. phalloides and the "Destroying Angel" A. bisporigera, were obtained. Each species has ~30 MSDIN genes, most of which are predicted to encode unknown cyclic peptides. Some MSDIN genes were duplicated in one or the other species, but only three were common to both species. A gene encoding cycloamanide B, a previously described nontoxic cyclic heptapeptide, was also present in A. phalloides, but genes for antamanide and cycloamanides A, C, and D were not. In A. bisporigera, RNA expression was observed for 20 of the MSDIN family members. Based on their predicted sequences, novel cyclic peptides were searched for by LC/MS/MS in extracts of A. phalloides. The presence of two cyclic peptides, named cycloamanides E and F with structures cyclo(SFFFPVP) and cyclo(IVGILGLP), was thereby demonstrated. Of the MSDIN genes reported earlier from another specimen of A. bisporigera, 9 of 14 were not found in the current genome assembly. Differences between previous and current results for the complement of MSDIN genes and cyclic peptides in the two fungi probably represents natural variation among geographically dispersed isolates of A. phalloides and among the members of the poorly defined A. bisporigera species complex. Both A. phalloides and A. bisporigera contain two prolyl oligopeptidase genes, one of which (POPB) is probably dedicated to cyclic peptide biosynthesis as it is in Galerina marginata. Conclusion: The MSDIN gene family has expanded and diverged rapidly in Amanita section Phalloideae. Together, A. bisporigera and A. phalloides are predicted to have the capacity to make more than 50 cyclic hexa-, hepta-, octa-, nona- and decapeptides. [ABSTRACT FROM AUTHOR]

Species in the mushroom genus Lepiota can cause fatal mushroom poisonings due to their content of amatoxins such as α-amanitin. Previous studies of the toxin composition of poisonous Lepiota species relied on analytical methods of low sensitivity or resolution. Using liquid chromatography coupled to UV absorbance and mass spectrometry, we analyzed the spectrum of peptide toxins present in six Italian species of Lepiota, including multiple samples of three of them collected in different locations. Field taxonomic identifications were confirmed by sequencing of the internal transcribed spacer (ITS) regions. For comparison, we also analyzed specimens of Amanita phalloides from Italy and California, a specimen of A. virosa from Italy, and a laboratory-grown sample of Galerina marginata. α-Amanitin, β-amanitin, amanin, and amaninamide were detected in all samples of L. brunneoincarnata, and α-amanitin and γ-amanitin were detected in all samples of L. josserandii. Phallotoxins were not detected in either species. No amatoxins or phallotoxins were detected in L. clypeolaria, L. cristata, L. echinacea, or L. magnispora. The Italian and California isolates of A. phalloides had similar profiles of amatoxins and phallotoxins, although the California isolate contained more β-amanitin relative to α-amanitin. Amaninamide was detected only in A. virosa. [ABSTRACT FROM AUTHOR]

Amatoxins, the lethal constituents of poisonous mushrooms in the genus Amanita, are bicyclic octapeptides. Two genes in A. bisporigera, AMA1 and PHA1, directly encode α-amanitin, an âmatoxin, and the related bicyclic heptapeptide phallacidin, a phallotoxin, indicating that these compounds are synthesized on ribosomes and not by nonribosomal peptide synthetases. α-Amanitin and phallacidin are synthesized as proproteins of 35 and 34 amino acids, respectively, from which they are predicted to be cleaved by a prolyl oligopeptidase. AMA1 and PHA1 are present in other toxic species of Amanita section Phalloidae but are absent from nontoxic species in other sections. The genomes of A. bisporigera and A. phalloides contain multiple sequences related to AMA1 and PHA1. The predicted protein products of this family of genes are characterized by a hypervariable "toxin" region capable of encoding a wide variety of peptides of 7-10 amino acids flanked by conserved sequences. Our results suggest that these fungi have a broad capacity to synthesize cyclic peptides on ribosomes. [ABSTRACT FROM AUTHOR]