Heterologous production of bioactive xenoacremone analogs in Aspergillus nidulans

Tyrosine-decahydrofluorene derivatives are a class of hybrid compounds that integrate the properties of polyketides and nonribosomal peptides.These compounds feature a[6.5.6]tricarbocyclic core and a para-cyclophane ether moiety in their structures and exhibit anti-tumor and anti-microbial activities.In this study,we constructed the biosynthetic pathway of xenoacremones from Xenoacremonium sinensis ML-31 in the Aspergillus nidulans host,resulting in the identification of four novel tyrosine-decahydrofluorene analogs,xenoacremones I–L(1-4),along with two known analogs,xenoacremones A and B.Remarkably,compounds 3 and 4 contained a 12-membered para-cyclophane ring system,which is unprecedented among tyrosine-decahydrofluorene analogs in X.sinensis.The successful reconstruction of the biosynthetic pathway and the discovery of novel analogs demonstrate the utility of heterologous expression strategy for the generation of structurally diverse natural products with potential biological activities.

Tricarbocyclic core formation of tyrosine-decahydrofluorenes implies a three-enzyme cascade with XenF-mediated sigmatropic rearrangement as a prerequisite

Tyrosine-decahydrofluorene derivatives feature a fused[6.5.6]tricarbocyclic core and a 13-membered para-cyclophane ether.Herein,we identified new xenoacremones A,B,and C(1-3)from the fungal strain Xenoacremonium sinensis ML-31 and elucidated their biosynthetic pathway using gene deletion in the native strain and heterologous expression in Aspergillus nidulans.The hybrid polyketide synthaseenonribosomal peptide synthetase(PKS-NRPS)XenE together with enoyl reductase XenG were confirmed to be responsible for the formation of the tyrosine-nonaketide skeleton.This skeleton was subsequently dehydrated by XenA to afford a pyrrolidinone moiety.XenF catalyzed a novel sigmatropic rearrangement to yield a key cyclohexane intermediate as a prerequisite for the formation of the multi-ring system.Subsequent oxidation catalyzed by XenD supplied the substrate for XenC to link the para-cyclophane ether,which underwent subsequent spontaneous Diels-Alder reaction to give the end products.Thus,the results indicated that three novel enzymes XenF,XenD,and XenC coordinate to assemble the[6.5.6]tricarbocyclic ring and para-cyclophane ether during biosynthesis of complex tyrosine-decahydrofluorene derivatives.