Diversity of MSDIN family members in amanitin-producing mushrooms and the phylogeny of the MSDIN and prolyl oligopeptidase genes.

BACKGROUND: Amanitin-producing mushrooms, mainly distributed in the genera Amanita, Galerina and Lepiota, possess MSDIN gene family for the biosynthesis of many cyclopeptides catalysed by prolyl oligopeptidase (POP). Recently, transcriptome sequencing has proven to be an efficient way to mine MSDIN and POP genes in these lethal mushrooms. Thus far, only A. palloides and A. bisporigera from North America and A. exitialis and A. rimosa from Asia have been studied based on transcriptome analysis. However, the MSDIN and POP genes of many amanitin-producing mushrooms in China remain unstudied; hence, the transcriptomes of these speices deserve to be analysed. RESULTS: In this study, the MSDIN and POP genes from ten Amanita species, two Galerina species and Lepiota venenata were studied and the phylogenetic relationships of their MSDIN and POP genes were analysed. Through transcriptome sequencing and PCR cloning, 19 POP genes and 151 MSDIN genes predicted to encode 98 non-duplicated cyclopeptides, including α-amanitin, ß-amanitin, phallacidin, phalloidin and 94 unknown peptides, were found in these species. Phylogenetic analysis showed that (1) MSDIN genes generally clustered depending on the taxonomy of the genus, while Amanita MSDIN genes clustered depending on the chemical substance; and (2) the POPA genes of Amanita, Galerina and Lepiota clustered and were separated into three different groups, but the POPB genes of the three distinct genera were clustered in a highly supported monophyletic group. CONCLUSIONS: These results indicate that lethal Amanita species have the genetic capacity to produce numerous cyclopeptides, most of which are unknown, while lethal Galerina and Lepiota species seem to only have the genetic capacity to produce α-amanitin. Additionally, the POPB phylogeny of Amanita, Galerina and Lepiota conflicts with the taxonomic status of the three genera, suggesting that underlying horizontal gene transfer has occurred among these three genera.

Characterization of a dual function macrocyclase enables design and use of efficient macrocyclization substrates.

Peptide macrocycles are promising therapeutic molecules because they are protease resistant, structurally rigid, membrane permeable, and capable of modulating protein-protein interactions. Here, we report the characterization of the dual function macrocyclase-peptidase enzyme involved in the biosynthesis of the highly toxic amanitin toxin family of macrocycles. The enzyme first removes 10 residues from the N-terminus of a 35-residue substrate. Conformational trapping of the 25 amino-acid peptide forces the enzyme to release this intermediate rather than proceed to macrocyclization. The enzyme rebinds the 25 amino-acid peptide in a different conformation and catalyzes macrocyclization of the N-terminal eight residues. Structures of the enzyme bound to both substrates and biophysical analysis characterize the different binding modes rationalizing the mechanism. Using these insights simpler substrates with only five C-terminal residues were designed, allowing the enzyme to be more effectively exploited in biotechnology.

Amanitinas / Amanitines

La intoxicación por consumo de hongos es un fenómeno estacional que se produce con relativa frecuencia en áreas geográficas donde es habitual su consumo, en especial de especies silvestres. Dependiendo del tipo de hongo ingerido pueden aparecer distintos cuadros clínicos (gastrointestinal, nefrotóxico, alucinatorio, etc.). El cuadro más grave es el hepatotóxico, asociado a una alta mortalidad, y causado por hongos que contienen amatoxinas (síndrome ciclopeptídico). Presentamos una revisión actualizada de las características de las amatoxinas, su cinética y mecanismo de acción, los métodos utilizados para su determinación analítica, así como las diferentes opciones para el tratamiento de la intoxicación (AU)

Mushroom poisoning is a seasonal phenomenon that occurs relatively frequently in geographical areas where its consumption is common. Depending on the type of fungus ingested different clinical symptoms (gastrointestinal, nephrotoxic, hallucinatory, etc.) can occur. Hepatotoxic syndrome caused by fungi containing amatoxins is the most serious condition, associated to high mortality. We present an updated review of amatoxins characteristics, kinetics, mechanism of action, methods used for analytical determination, as well as the different options for the treatment of poisoning (AU)

Amatoxin and phallotoxin concentration in Amanita phalloides spores and tissues.

Most of the fatal cases of mushroom poisoning are caused by Amanita phalloides. The amount of toxin in mushroom varies according to climate and environmental conditions. The aim of this study is to measure α-, ß-, and γ-amanitin with phalloidin and phallacidin toxin concentrations. Six pieces of A. phalloides mushrooms were gathered from a wooded area of Düzce, Turkey, on November 23, 2011. The mushrooms were broken into pieces as spores, mycelium, pileus, gills, stipe, and volva. α-, ß-, and γ-Amanitin with phalloidin and phallacidin were analyzed using reversed-phase high-performance liquid chromatography. As a mobile phase, 50 mM ammonium acetate + acetonitrile (90 + 10, v/v) was used with a flow rate of 1 mL/min. C18 reverse phase column (150 × 4.6 mm; 5 µm particle) was used. The least amount of γ-amanitin toxins was found at the mycelium. The other toxins found to be in the least amount turned out to be the ones at the spores. The maximum amounts of amatoxins and phallotoxin were found at gills and pileus, respectively. In this study, the amount of toxin in the spores of A. phalloides was published for the first time, and this study is pioneering to deal with the amount of toxin in mushrooms grown in Turkey.

Peptide macrocyclization catalyzed by a prolyl oligopeptidase involved in α-amanitin biosynthesis.

Amatoxins are ribosomally encoded and posttranslationally modified peptides that account for the majority of fatal mushroom poisonings of humans. A representative amatoxin is the bicyclic octapeptide α-amanitin, formed via head-to-tail macrocyclization, which is ribosomally biosynthesized as a 35-amino acid propeptide in Amanita bisporigera and in the distantly related mushroom Galerina marginata. Although members of the prolyl oligopeptidase (POP) family of serine proteases have been proposed to play a role in α-amanitin posttranslational processing, the exact mechanistic details are not known. Here, we show that a specific POP (GmPOPB) is required for toxin maturation in G. marginata. Recombinant GmPOPB catalyzed two nonprocessive reactions: hydrolysis at an internal Pro to release the C-terminal 25-mer from the 35-mer propeptide and transpeptidation at the second Pro to produce the cyclic octamer. On the other hand, we show that GmPOPA, the putative housekeeping POP of G. marginata, behaves like a conventional POP.

Ribosomal biosynthesis of the cyclic peptide toxins of Amanita mushrooms.

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.

Gene family encoding the major toxins of lethal Amanita mushrooms.

Amatoxins, the lethal constituents of poisonous mushrooms in the genus Amanita, are bicyclic octapeptides. Two genes in A. bisporigera, AMA1 and PHA1, directly encode alpha-amanitin, an amatoxin, and the related bicyclic heptapeptide phallacidin, a phallotoxin, indicating that these compounds are synthesized on ribosomes and not by nonribosomal peptide synthetases. alpha-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.

Production and characterization of Amanitin toxins from a pure culture of Amanita exitialis.

Amanita exitialis Zhu L. Yang and T.H. Li is a lethal mushroom species recently isolated in Guangdong Province, China. In this report, a pure culture of this species was obtained for the first time. To confirm the identity of the pure culture, the internal transcribed spacer regions of the nuclear ribosomal DNA of the pure culture and of a typical fruiting body of the species were sequenced and compared. Further, amatoxins produced by pure cultures were analyzed and characterized by high-performance liquid chromatography and mass spectrometry analysis. The results showed that the pure cultures produced 728.3 +/- 43.8 microg g(-1) (dry matter) of alpha-Amanitin and 60.0 +/- 20.7 microg g(-1) (dry matter) of beta-Amanitin, respectively, a yield which is about 10% of that produced by fruiting bodies.

Unique amanitin resistance of RNA synthesis in isolated nuclei from Amanita species accumulating amanitins.

In order to understand the basis upon which amanitin-accumulating species of Amanita are able to develop in the presence of these specific inhibitors of RNA synthesis, the in vitro RNA synthesizing activities of nuclei isolated from amanitin-accumulating species. Amanita hygroscopica (culture, derived from amanitin-accumulating carpophore) and A. suballiacea (carpophore), and from the non-accumulating species A. solitaria (culture) and A. brunnescens (carpophore) were tested for their sensitivities to alpha-amanitin inhibition. The nuclear RNA synthesizing activities obtained from both carpophores and cultures of non-accumulating organisms displayed significant sensitivities to alpha-amanitin, whereas those obtained from accumulating organisms displayed remarkable resistance to alpha-amanitin. The observed relationship between levels of amanitins in carpophores and resistance of the RNA synthesizing activities to inhibition by alpha-amanitin supports the hypothesis that amanitins may function as regulators of mRNA transcription in Amanita species.