Novel Cyclic Peptides from Lethal Mushrooms through a Genome-Guided Approach.

Most species in the genus are ectomycorrhizal fungi comprising both edible and poisonous mushrooms. Some species produce potent cyclic peptide toxins, such as α-amanitin, which places them among the deadliest organisms known to mankind. These toxins and related cyclic peptides are encoded by genes of the "MSDIN" family (named after the first five amino acid residues of the precursor peptides), and it is largely unknown to what extent these genes are expressed in the basidiocarps. In the present study, and were sequenced through the PacBio and Illumina techniques. Together with our two previously sequenced genomes, and , in total, 46 previously unknown genes were discovered. The expression of over 80% of the genes was demonstrated in . Through a combination of genomics and mass spectrometry, 12 genes were shown to produce novel cyclic peptides. To further confirm the results, three of the cyclic peptides were chemically synthesized. The tandem mass spectrometry (MS/MS) spectra of the natural and the synthetic peptides shared a majority of the fragment ions, demonstrating an identical structure between each peptide pair. Collectively, the results suggested that the genome-guided approach is reliable for identifying novel cyclic peptides in species and that there is a large peptide reservoir in these mushrooms.