What Makes Certain Mushrooms 'Magic'?

In a recent study published in the journal Nature Communications, an international research team from various Universities including Hans Knöll Institute investigated the biosynthesis of psilocybin, the primary component of hallucinogenic mushrooms.

The team acquired fresh knowledge regarding the composition and mode of action of the PsiM enzyme. It is essential in the synthesis of psilocybin.

The primary natural product of the genus Psilocybe, commonly known as "magic mushrooms," is the psychoactive compound psilocybin, which makes these mushrooms a well-liked drug. In recent times, psilocybin has garnered significant interest in medicine as a potential treatment for several mental disorders.

It has demonstrated encouraging outcomes when treating anxiety, addiction, and depression. Psilocybin is already in an advanced stage of clinical testing as an active pharmaceutical ingredient.

Fungi use intricate biochemical processes to convert the amino acid L-tryptophan into psilocybin. Methyltransferase PsiM is an essential component of this process. It catalyzes the final two steps in the synthesis of psilocybin, which are two consecutive methylation reactions.

There are many methyl transfer reactions in nature. Here, we asked ourselves how exactly psilocybin production is accomplished.”

Dirk Hoffmeister, Professor, Pharmaceutical Microbiology, Friedrich Schiller University

Hoffmeister also heads an associated research group at the Leibniz Institute for Natural Product Research and Infection Biology - Hans Knöll Institute (Leibniz-HKI)

Two Enzymes, One Origin

Towards this aim, a group from the Medical University of Innsbruck, under the direction of Crystallographer Bernhard Rupp and the Jena scientists, examined the enzyme PsiM through biochemical and X-ray crystal structure analysis. Using this technique, multiple reaction stages could be shown in extremely high resolution, and proteins could be seen down to the atomic level.

Analysis of the protein structure showed that the fungal enzyme PsiM and enzymes are typically in charge of RNA modification and share striking structural similarities.

The strong structural similarity suggests that the fungal enzyme evolved from a single methylating RNA methyltransferase, despite the fact that there are some differences as well.

As such, its previous capacity to bind a single methyl group to the target molecule was limited.

The psilocybin precursor norbaeocystin, which is converted by PsiM, structurally imitates part of the RNA, but is methylated twice.”

Dirk Hoffmeister, Professor, Pharmaceutical Microbiology, Friedrich Schiller University, Jena

A Small Swap With a Big Impact

Through additional research, the scientists also discovered an essential amino acid swap that allowed PsiM to perform double methylation during evolution.

The conversion of the single-methylated intermediate baeocystin to the double-methylated psilocybin is the last step in the reaction chain for the possible biotechnological synthesis of the active ingredient.

A Clear End

The researchers then investigated if PsiM could add a third methyl group to transform psilocybin into aeruginascin. An analog of psilocybin, which is found naturally in certain types of fungi, is aeruginascin.

Hoffmeister asks, “The only question is, where does it come from?”

The scientific community has disagreed on whether the substance is a metabolic byproduct of the psilocybin biosynthesis pathway or if it can originate from psilocybin through PsiM.

The study now provides a clear result. 

This is clearly not the case. PsiM is not able to convert psilocybin to aeruginascin.”

Dirk Hoffmeister, Professor, Pharmaceutical Microbiology, Friedrich Schiller University, Jena

Therefore, PsiM cannot be involved in the biosynthetic synthesis of this analog. On the other hand, the enzyme might be important for future psilocybin production in microorganisms. Hoffmeister said, “Overall, our results can help to develop new variants of psilocybin with improved therapeutic properties and to produce them biotechnologically.”