In Search Of Novel Amanita Cyclic Peptides Through Application Of A Genome-Guided Approach

Most species in the genus Amanita(Amanitaceae,Agaricales)are ectomycorrhizal fungi,which comprise both famous edible mushrooms and many poisonous species.The toxins in the poisonous Amanita species mainly fall into three categories,i.e.,causing hepatic failure,renal failure,or hallucinogenic.The toxins that lead to hepatic failure belong to Amanita cyclic peptides,mainly including amatoxins and phallotoxins.Amatoxins are highly specific with extremely low lethal dose,and one mushroom fruiting body that contains these toxins is enough to cause death in an adult.Worldwide,over 90% of lethal mushroom poisonings are due to amatoxins,while in China,68.0-90.9% of the deadly cases are caused by the toxins based on China CDC's data.Amanita cyclic peptides are encoded by MSDIN gene(named after the first five amino acid residues of the precursor peptides)family.Many MSDIN genes exist but it is largely unknown whether these genes are expressed,nor whether there are corresponding cyclic peptides.In the present study,Amanita subjunquillea,A.pallidorosea,A.rimosa and A.exitialis were studied to address the above-mentioned questions based on our genomic platform.The main conclusions are listed as the following:1.High-quality draft genomes for A.rimosa and A.exitialis were obtained through Pac Bio and Illumina techniques.Together with our previously sequenced genomes of A.subjunquillea and A,pallidorosea,in total 66 MSDIN genes were obtained,of which 46 were novel.In addition,expression of over 80% of the MSDIN genes was demonstrated in A.subjunquillea.2.To investigate whether the expressed MSDIN genes further give rise to novel Amanita cyclic peptides,putative cyclic peptides were predicted based on genomic data.In total,12 novel(Cyl G1,Cyl G2,Cyl H1,Cyl H2,Cyl H3,Cyl J1,Cyl J2,Cyl I1,Cyl I2,Cyll3,Cyl I4,and Cyl I5)and one known(amanexitide)cyclic peptides were confirmed through a combination of analyses on the fragment ions,including high-res MS(MS/MS),and automated and manual pipelines on fragment ions.3.The reliability of the results was furthered confirmed by chemically synthesizing two novel cyclic peptides,Cyl G1 and Cyl G2,and the known amanexitide peptide.By comparing fragment ions of the natural peptides with synthetic ones in MS/MS analyses,we found that most ions are identical in both cases,clearly showing that the peptide pairs have identical structures.Our study provides a genome-guided approach for fast identification of Amanita cyclic peptides.The results obtained many novel cyclic peptides,which indicates that there is a large cyclic peptide reservoir in Amanita species.This study provides an important foundation for further application of Amanita cyclic peptides.