Exploring the biocatalysis of psilocybin and other tryptamines: Enzymatic pathways, synthetic strategies, and industrial implications

Tryptamines play diverse roles as neurotransmitters and psychoactive compounds found in various organisms. Psilocybin, a notable tryptamine, has garnered attention for its therapeutic potential in treating mental health disorders like depression and anxiety. Despite its promising applications, current extraction methods for psilocybin are labor-intensive and economically limiting. We suggest biocatalysis as a sustainable alternative, leveraging enzymes to synthesize psilocybin and other tryptamines efficiently. By elucidating psilocybin biosynthesis pathways, researchers aim to advance synthetic methodologies and industrial applications. This review underscores the transformative potential of biocatalysis in enhancing our understanding of tryptamine biosynthesis and facilitating the production of high-purity psilocybin and other tryptamines for therapeutic and research use.

Evaluation of TrpM and PsiD substrate promiscuity reveals new biocatalytic capabilities

N-methylated tryptamines, such as the hallucinogenic natural products, psilocybin and N,N-dimethyltryptamine (DMT), are gaining interest from the medical community due to their potential as next generation treatments for mental health disorders. The clinical relevance of these compounds has driven scientists to develop biosynthetic production routes to a number of tryptamine drug candidates, and efforts are ongoing to expand and further develop these biosynthetic capabilities. To that end, we have further characterized the substrate preferences of two enzymes involved in tryptamine biosynthesis: TrpM, a tryptophan N-methyltransferase from Psilocybe serbica, and PsiD, the gateway decarboxylase of the psilocybin biosynthesis pathway. Here, we show that TrpM can N-methylate the non-native amino acid substrate, 4-hydroxytryptophan, a key intermediate in the Escherichia coli-based recombinant psilocybin biosynthesis pathway. However, the ability to incorporate TrpM into a functional psilocybin biosynthesis pathway was thwarted by PsiD's inability to use N,N-dimethyl-4-hydroxytryptophan as substrate, under the culturing conditions tested, despite demonstrating activity on N-methylated and 4-hydroxylated tryptophan derivatives individually. Taken together, this work expands upon the known substrates for TrpM and PsiD, further increasing the diversity of tryptamine biosynthetic products.

Methyl transfer in psilocybin biosynthesis

Psilocybin, the natural hallucinogen produced by Psilocybe ("magic") mushrooms, holds great promise for the treatment of depression and several other mental health conditions. The final step in the psilocybin biosynthetic pathway, dimethylation of the tryptophan-derived intermediate norbaeocystin, is catalysed by PsiM. Here we present atomic resolution (0.9 Å) crystal structures of PsiM trapped at various stages of its reaction cycle, providing detailed insight into the SAM-dependent methylation mechanism. Structural and phylogenetic analyses suggest that PsiM derives from epitranscriptomic N6-methyladenosine writers of the METTL16 family, which is further supported by the observation that bound substrates physicochemically mimic RNA. Inherent limitations of the ancestral monomethyltransferase scaffold hamper the efficiency of psilocybin assembly and leave PsiM incapable of catalysing trimethylation to aeruginascin. The results of our study will support bioengineering efforts aiming to create novel variants of psilocybin with improved therapeutic properties.

A cane toad (Rhinella marina) N-methyltransferase converts primary indolethylamines to tertiary psychedelic amines

Psychedelic indolethylamines have emerged as potential medicines to treat several psychiatric pathologies. Natural sources of these compounds include 'magic mushrooms' (Psilocybe spp.), plants used to prepare ayahuasca, and toads. The skin and parotid glands of certain toads accumulate a variety of specialized metabolites including toxic guanidine alkaloids, lipophilic alkaloids, poisonous steroids, and hallucinogenic indolethylamines such as DMT, 5-methoxy-DMT, and bufotenin. The occurrence of psychedelics has contributed to the ceremonial use of toads, particularly among Mesoamerican peoples. Yet, the biosynthesis of psychedelic alkaloids has not been elucidated. Herein, we report a novel indolethylamine N-methyltransferase (RmNMT) from cane toad (Rhinella marina). The RmNMT sequence was used to identify a related NMT from the common toad, Bufo bufo. Close homologs from various frog species were inactive, suggesting a role for psychedelic indolethylamine biosynthesis in toads. Enzyme kinetic analyses and comparison with functionally similar enzymes showed that recombinant RmNMT was an effective catalyst and not product inhibited. The substrate promiscuity of RmNMT enabled the bioproduction of a variety of substituted indolethylamines at levels sufficient for purification, pharmacological screening, and metabolic stability assays. Since the therapeutic potential of psychedelics has been linked to activity at serotonergic receptors, we evaluated binding of derivatives at 5-HT1A and 5-HT2A receptors. Primary amines exhibited enhanced affinity at the 5-HT1A receptor compared with tertiary amines. With the exception of 6-substituted derivatives, N,N-dimethylation also protected against catabolism by liver microsomes.

In silico characterization of the psilocybin biosynthesis pathway

Nearly all mushrooms of the Psilocybe genus contain the natural product psilocybin, which is a psychoactive alkaloid derived from l-tryptophan. Considering their use in ancient times, as well as their psychedelic properties, these mushrooms have re-emerged with psychotherapeutic potential for treating depression, which has triggered increased pharmaceutical interest. However, the psilocybin biosynthesis pathway was only recently defined and, as such, little exists in the way of structural data. Accordingly, the aim of this study was to structurally characterize this pathway by generating homology models for the four Psilocybe cubensis enzymes involved in psilocybin biosynthesis (PsiD, a decarboxylase; PsiH, a monooxygenase; PsiK, a phosphotransferase; PsiM, a methyltransferase). Following initial model generation and alignment with the identified structural templates, repeated refinement of the models was carried out using secondary structure prediction, geometry evaluation, energy minimization, and molecular dynamics simulations in water. The final models were then evaluated using molecular docking interactions with their substrates, i.e., psilocybin precursors (l-tryptophan, tryptamine, 4-hydroxytryptamine, and norbaeocystin/baeocystin), all of which generated feasible binding modes for the expected biotransformation. Further plausibility of the psilocybin → aeruginascin, 4-hydroxytryptamine → norpsilocin, and tryptamine → N,N-dimethyltryptamine conversions, all mediated by the generated model for PsiM, suggests valid routes of formation for these key secondary metabolites. The structural characterization of these enzymes and their binding modes which emerged from this study can lead to a better understanding of psilocybin synthesis, thereby paving the way for the development of novel substrates and selective inhibitors, as well as improved biotechnological manipulation and production of psilocybin in vitro.

Characterization of the Gateway Decarboxylase for Psilocybin Biosynthesis

The l-tryptophan decarboxylase PsiD catalyzes the initial step of the metabolic cascade to psilocybin, the major indoleethylamine natural product of the "magic" mushrooms and a candidate drug against major depressive disorder. Unlike numerous pyridoxal phosphate (PLP)-dependent decarboxylases for natural product biosyntheses, PsiD is PLP-independent and resembles type II phosphatidylserine decarboxylases. Here, we report on the in vitro biochemical characterization of Psilocybe cubensis PsiD along with in silico modeling of the PsiD structure. A non-canonical serine protease triad for autocatalytic cleavage of the pro-protein was predicted and experimentally verified by site-directed mutagenesis.

Psilocybin containing mushrooms: a rapidly developing biotechnology industry in the psychiatry, biomedical and nutraceutical fields

Humans have collected and used hallucinogenic mushrooms for ethnic medicinal, recreational, and religious purposes since before recorded history. Currently, the use of these mushrooms is illegal in most countries, but where their use is legal they are applied as self medication. Psilocybin and psilocin, two psychoactive alkaloids, are naturally synthesized by hallucinogenic mushrooms. The chemical structure of these compounds are similar to the neurotransmitter serotonin. Activation of this system by psilocybin and psilocin may produce temporary changes in the brain that induce hallucinations and feelings of euphoria. Adjustment of the serotonin system in this way can moderate symptoms of related mental disorders. This review summarizes relevant and current information regarding the discovery of hallucinogenic mushrooms and their contained psychoactive compounds, the events that lead to their criminalization and decriminilization, and the state of knowledge of psilocybin, psilocin, and derivatives. Last, research on the psychoactive properties of these mushrooms is placed in perspective to possible applications for human dysfunctions.

Methyltransferases: Functions and Applications

In this review the current state-of-the-art of S-adenosylmethionine (SAM)-dependent methyltransferases and SAM are evaluated. Their structural classification and diversity is introduced and key mechanistic aspects presented which are then detailed further. Then, catalytic SAM as a target for drugs, and approaches to utilise SAM as a cofactor in synthesis are introduced with different supply and regeneration approaches evaluated. The use of SAM analogues are also described. Finally O-, N-, C- and S-MTs, their synthetic applications and potential for compound diversification is given.

Recent Advances in the Synthesis of Marine-Derived Alkaloids via Enzymatic Reactions

Alkaloids are a large and structurally diverse group of marine-derived natural products. Most marine-derived alkaloids are biologically active and show promising applications in modern (agro)chemical, pharmaceutical, and fine chemical industries. Different approaches have been established to access these marine-derived alkaloids. Among these employed methods, biotechnological approaches, namely, (chemo)enzymatic synthesis, have significant potential for playing a central role in alkaloid production on an industrial scale. In this review, we discuss research progress on marine-derived alkaloid synthesis via enzymatic reactions and note the advantages and disadvantages of their applications for industrial production, as well as green chemistry for marine natural product research.

The phosphate ester group in secondary metabolites

Covering: 2000 to mid-2021The phosphate ester is a versatile, widespread functional group involved in a plethora of biological activities. Its presence in secondary metabolites, however, is relatively rare compared to other functionalities and thus is part of a rather unexplored chemical space. Herein, the chemistry of secondary metabolites containing the phosphate ester group is discussed. The text emphasizes their structural diversity, biological and pharmacological profiles, and synthetic approaches employed in the phosphorylation step during total synthesis campaigns, covering the literature from 2000 to mid-2021.

A draft reference assembly of the Psilocybe cubensis genome

We describe the use of high-fidelity single molecule sequencing to assemble the genome of the psychoactive Psilocybe cubensis mushroom. The genome is 46.6Mb, 46% GC, and in 32 contigs with an N50 of 3.3Mb. The BUSCO completeness scores are 97.6% with 1.2% duplicates. The Psilocybin synthesis cluster exists in a single 3.2Mb contig. The dataset is available from NCBI BioProject with accessions PRJNA687911 and PRJNA700437.

Chemoenzymatic Synthesis of 5-Methylpsilocybin: A Tryptamine with Potential Psychedelic Activity

A novel analogue of psilocybin was produced by hybrid chemoenzymatic synthesis in sufficient quantity to enable bioassay. Utilizing purified 4-hydroxytryptamine kinase from Psilocybe cubensis, chemically synthesized 5-methylpsilocin (2) was enzymatically phosphorylated to provide 5-methylpsilocybin (1). The zwitterionic product was isolated from the enzymatic step with high purity utilizing a solvent-antisolvent precipitation approach. Subsequently, 1 was tested for psychedelic-like activity using the mouse head-twitch response assay, which indicated activity that was more potent than the psychedelic dimethyltryptamine, but less potent than that of psilocybin.

Mind the mushroom: natural product biosynthetic genes and enzymes of Basidiomycota

Covering: up to September 2020 Mushroom-forming fungi of the division Basidiomycota have traditionally been recognised as prolific producers of structurally diverse and often bioactive secondary metabolites, using the methods of chemistry for research. Over the past decade, -omics technologies were applied on these fungi, and sophisticated heterologous gene expression platforms emerged, which have boosted research into the genetic and biochemical basis of the biosyntheses. This review provides an overview on experimentally confirmed natural product biosyntheses of basidiomycete polyketides, amino acid-derived products, terpenoids, and volatiles. We also present challenges and solutions particular to natural product research with these fungi. 222 references are cited.

Taking Different Roads: l-Tryptophan as the Origin of Psilocybe Natural Products

Psychotropic fungi of the genus Psilocybe, colloquially referred to as "magic mushrooms", are best known for their l-tryptophan-derived major natural product, psilocybin. Yet, recent research has revealed a more diverse secondary metabolism that originates from this amino acid. In this minireview, the focus is laid on l-tryptophan and the various Psilocybe natural products and their metabolic routes are highlighted. Psilocybin and its congeners, the heterogeneous blue-colored psilocyl oligomers, alongside β-carbolines and N,N-dimethyl-l-tryptophan, are presented as well as current knowledge on their biosynthesis is provided. The multidisciplinary character of natural product research is demonstrated, and pharmacological, medicinal, ecological, biochemical, and evolutionary aspects are included.

Scalable Hybrid Synthetic/Biocatalytic Route to Psilocybin

Psilocybin, the principal indole alkaloid of Psilocybe mushrooms, is currently undergoing clinical trials as a medication against treatment-resistant depression and major depressive disorder. The psilocybin supply for pharmaceutical purposes is met by synthetic chemistry. We replaced the problematic phosphorylation step during synthesis with the mushroom kinase PsiK. This enzyme was biochemically characterized and used to produce one gram of psilocybin from psilocin within 20 minutes. We also describe a pilot-scale protocol for recombinant PsiK that yielded 150 mg enzyme in active and soluble form. Our work consolidates the simplicity of tryptamine chemistry with the specificity and selectivity of enzymatic catalysis and helps provide access to an important drug at potentially reasonable cost.

S-Adenosyl-l-Methionine Salvage Impacts Psilocybin Formation in "Magic" Mushrooms

Psychotropic Psilocybe mushrooms biosynthesize their principal natural product psilocybin in five steps, among them a phosphotransfer and two methyltransfer reactions, which consume one equivalent of 5'-adenosine triphosphate (ATP) and two equivalents of S-adenosyl-l-methionine (SAM). This short but co-substrate-intensive pathway requires nucleoside cofactor salvage to maintain high psilocybin production rates. We characterized the adenosine kinase (AdoK) and S-adenosyl-l-homocysteine (SAH) hydrolase (SahH) of Psilocybe cubensis. Both enzymes are directly or indirectly involved in regenerating SAM. qRT-PCR expression analysis revealed an induced expression of the genes in the fungal primordia and carpophores. A one-pot in vitro reaction with the N-methyltransferase PsiM of the psilocybin pathway demonstrates a concerted action with SahH to facilitate biosynthesis by removal of accumulating SAH.