A bacterial-like Pictet–Spenglerase drives the evolution of fungi to produce β-carboline glycosides together with separate genes

Abstract

Diverse β-carboline (βC) alkaloids are produced by microbes, plants, and animals with myriad bioactivities and drug potentials. However, the biosynthetic mechanism of βCs remains largely elusive, especially regarding the hydroxyl and glucosyl modifications of βCs. Here, we report the presence of the bacterial-like Pictet–Spenglerase gene Fcs1 in the entomopathogenic Beauveria fungi that can catalyze the biosynthesis of the βC skeleton. The overexpression of Fcs1 in Beauveria bassiana led to the identification of six βC methyl glycosides, termed bassicarbosides (BCSs) A–F. We verified that the cytochrome P450 (CYP) genes adjacent to Fcs1 cannot oxidize βCs. Alternatively, the separated CYP684B2 family gene Fcs2 was identified to catalyze βC hydroxylation together with its cofactor gene Fcs3 . The functional homologue of Fcs2 is only present in the Fcs1- containing fungi and highly similar to the Fcs1- connected yet nonfunctional CYP. Both evolved quicker than those from fungi without Fcs1 homologues. Finally, the paired methyl/glucosyl transferase genes were verified to mediate the production of BCSs from hydroxy-βCs. All these functionally verified genes are located on different chromosomes of Beauveria , which is in contrast to the typical content-clustered feature of fungal biosynthetic gene clusters (BGCs). We also found that the production of BCSs selectively contributed to fungal infection of different insect species. Our findings shed light on the biosynthetic mechanism of βC glycosides, including the identification of a βC hydroxylase. The results of this study also propose an evolving process of fungal BGC formation following the horizontal transfer of a bacterial gene to fungi.

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“…40 One example of this approach was the recent identification of a fungal Pictet-Spenglerase (PS) using the bacterial PS McbB from the marinacarboline biosynthesis. 41 There are significant implications to finally establishing the gene−metabolite link of 1. In East Asia, mycotoxins produced by koji mold A. oryzae are especially concerning since many Asian foods and seasonings including soy sauce and miso are produced from the fermentation of ingredients with A. oryzae.…”

“…While such examples of “cross-kingdom genome mining” for secondary metabolism BGCs are still limited, this approach could be fruitful to identify the BGCs of metabolites that are not biosynthesized from canonical core enzymes . One example of this approach was the recent identification of a fungal Pictet-Spenglerase (PS) using the bacterial PS McbB from the marinacarboline biosynthesis …”

How Fungi Biosynthesize 3-Nitropropanoic Acid: the Simplest yet Lethal Mycotoxin

“…[54] One example of this approach was the recent identification of a fungal Pictet-Spenglerase (PS) using the bacterial PS McbB from the marinacarboline biosynthesis. [55] There are significant implications to finally establishing the gene-metabolite link of 1. In East Asia, mycotoxins produced by koji mold A. oryzae is especially concerning since many Asian food and seasonings including soy source and miso are produced from the fermentation of ingredients with A. oryzae.…”