Researchers have successfully unraveled the genetic code of *Penicillium citrinum*, a widely recognized mold found on citrus fruits. This breakthrough sheds light on how nature creates cyclopentachromone, a crucial component for bioactive substances that may have potential in cancer and inflammation therapies. The research team discovered a new enzyme, IscL, that produces a highly reactive sulfur-containing intermediate, enhancing our understanding of the chemistry within fungi. This finding could lead to innovative pharmaceuticals by utilizing nature’s biochemical mechanisms.
For nearly a hundred years, starting from Alexander Fleming’s accidental discovery of penicillin in 1928, fungi have emerged as a rich source of medicinal products. They have yielded treatments for a diverse array of ailments, ranging from infections and cholesterol issues to organ transplant rejection and even cancer.
Nonetheless, the mechanisms through which fungi generate some of their most effective compounds are still not fully understood. This lack of clarity particularly surrounds cyclopentachromone, a vital precursor in fungal-derived products with shown efficacy against cancer and inflammation, among other health benefits.
Decoding Nature’s Formula
Though chemists have made strides in synthesizing chromone variants in laboratories, replicating the unique structure of this molecule with accuracy has been challenging. “It’s quite common to end up with a version that has misplaced chemical bonds or a flipped structure,” explains Sherry Gao, Associate Professor in Chemical and Biomolecular Engineering (CBE) and Bioengineering (BE).
In a recent publication in the *Journal of the American Chemical Society*, Gao’s research group details how they decoded nature’s instructions by analyzing the genes of *Penicillium citrinum*, aiding in the discovery of an unreported enzyme that facilitates the synthesis of cyclopentachromone-containing compounds.
“Nature has spent billions of years evolving methods to synthesize these compounds,” remarks Gao, the lead author of the paper. “Now we can utilize nature’s tools to further develop and investigate these compounds, potentially leading to new pharmaceuticals.”
A Complex Chemical Structure
The uniqueness of cyclopentachromone lies in its special structure, which consists of three carbon rings—two with six carbons and one with five. Similar to the framework of a building, this arrangement forms the foundational structure for many bioactive molecules.
However, one known chemical precursor to cyclopentachromone has an additional carbon, resulting in three rings of identical size. The process by which nature transforms this compound into one with a different ring configuration—especially since such rings are generally stable—had not been previously described.
To uncover this process, the researchers systematically activated and deactivated genes in *P. citrinum* to identify disruptions in the pathway, revealing which genes are responsible for the active enzyme. “It was as if we had to test hundreds of switches to find out which one controls a specific light,” explains Qiuyue Nie, a postdoctoral fellow in the Gao Lab and the principal author of the study.
The researchers found that a different intermediate compound, 2S-remisporine A, produced by the newly discovered enzyme IscL, features a sulfur atom connected to one side of its three-ring framework, similar to a hitch on a truck.
From Nature to Healing
The high reactivity of this compound is what contributes to the medicinal possibilities of cyclopentachromone. Just as a truck can pull various attachments like trailers and boats, the carbon-sulfur bond in 2S-remisporine A can interact with a wide range of other groups, producing a variety of new molecules. “This intermediary compound is very reactive,” notes Nie. “The carbon-sulfur bond can engage with different sulfur donors, leading to the creation of many new compounds.”
The extreme reactivity of 2S-remisporine A, which can interact with numerous molecules, even itself, explains why its precursor has never been completely characterized until now. “We could not have devised a method to create such a reactive intermediate,” affirms Nie. “We needed to understand how nature produces it and then apply those enzymatic tools ourselves.”
The research team envisions that follow-up studies will trace this newly unearthed pathway using the genetic framework that directs it, aiming to advance the application of fungal compounds in medicine. “Nature presents a remarkable set of tools,” adds Gao. “This publication illustrates how one such tool is generated.”
The research was carried out at the University of Pennsylvania School of Engineering and Applied Science, supported by the National Institute of Health (R35GM138207) and startup funding from the University of Pennsylvania.
Other co-authors include Chunxiao Sun, Shuai Lu, and Maria Zotova from Penn Engineering, and Qiang Li and Tong Zhu from East China Normal University.
