Hubei International Scientific and Technological Cooperation Base of Traditional Fermented Foods, Key Laboratory of Environment Correlative Dietology, College of Food Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, China.
Southwest Center for Natural Products Research, College of Agriculture and Life Sciences, University of Arizona, Tucson, Arizona, USA.
mBio. 2020 Feb 4;11(1):e02676-19. doi: 10.1128/mBio.02676-19.
Despite the important biological activities of natural product naphthoquinones, the biosynthetic pathways of and resistance mechanisms against such compounds remain poorly understood in fungi. Here, we report that the genes responsible for the biosynthesis of naphthoquinones (monasones) reside within the gene cluster for azaphilone pigments (MonAzPs). We elucidate the biosynthetic pathway of monasones by a combination of comparative genome analysis, gene knockouts, heterologous coexpression, and and enzymatic reactions to show that this pathway branches from the first polyketide intermediate of MonAzPs. Furthermore, we propose that the monasone subset of biosynthetic genes also encodes a two-tiered resistance strategy in which an inducible monasone-specific exporter expels monasones from the mycelia, while residual intracellular monasones may be rendered nontoxic through a multistep reduction cascade. The genes for naphthoquinone (monasone) biosynthesis are embedded in and form a composite supercluster with the azaphilone pigment biosynthetic gene cluster. Early biosynthetic intermediates are shared by the two pathways. Some enzymes encoded by the supercluster play double duty in contributing to both pathways, while others are specific for one or the other pathway. The monasone subcluster is independently regulated and inducible by elicitation with competing microorganisms. This study illustrates genomic and biosynthetic parsimony in fungi and proposes a potential path for the evolution of the mosaic-like azaphilone-naphthoquinone supercluster. The monasone subcluster also encodes a two-tiered self-resistance mechanism that models resistance determinants that may transfer to target microorganisms or emerge in cancer cells in case of naphthoquinone-type cytotoxic agents.
尽管天然产物萘醌具有重要的生物活性，但真菌中此类化合物的生物合成途径和抗性机制仍知之甚少。在这里，我们报告负责萘醌（单甲萘醌）生物合成的基因位于氮杂菲酮色素（MonAzPs）的基因簇内。我们通过比较基因组分析、基因敲除、异源共表达和酶反应的组合阐明了单甲萘醌的生物合成途径，表明该途径从 MonAzPs 的第一个聚酮中间产物分支。此外，我们提出单甲萘醌生物合成基因簇的单甲萘醌亚簇还编码了一种两级抗性策略，其中诱导型单甲萘醌特异性外排泵将单甲萘醌从菌丝体中排出，而残留的细胞内单甲萘醌可能通过多步还原级联反应而变得无毒。萘醌（单甲萘醌）生物合成基因嵌入并与氮杂菲酮色素生物合成基因簇形成复合超基因簇。两种途径共享早期生物合成中间产物。超基因簇编码的一些酶在两种途径中都发挥双重作用，而其他酶则特异性地参与一种或另一种途径。单甲萘醌亚簇独立调控，并可通过与竞争微生物的诱导而诱导。这项研究说明了真菌中的基因组和生物合成简约性，并提出了氮杂菲酮-萘醌超基因簇进化的潜在途径。单甲萘醌亚簇还编码了一种两级自我抗性机制，该机制模拟了抗性决定因素，这些因素可能转移到靶微生物中，或者在出现萘醌型细胞毒性剂的情况下出现在癌细胞中。
