Reconstituting the complete biosynthesis of D-lysergic acid in yeast

Ergot alkaloids exert pharmacological effects due to the structural similarity of the ergoline scaffold to monoamine neurotransmitters, including adrenaline, dopamine, and serotonin. Consequently, ergot alkaloids and their derivatives are widely used to treat neurological disorders such as Parkinson’s disease, dementia, and hypertension. The key active pharmaceutical precursor for many of these derivatives is D-lysergic acid (DLA). Global demand for ergot alkaloids is substantial, with up to ~105 tons of DLA produced annually, largely via submerged fermentation of Claviceps purpurea or field cultivation. These conventional methods face significant drawbacks: (i) heterogeneous product mixtures complicate downstream extraction and raise production costs, and (ii) specialized producing strains are prone to degradation over time. Chemical total syntheses of DLA, while reported, are lengthy (up to 19 steps) and low-yielding (total yields a fraction of 12%); even the simpler 8-step routes have modest yield and lack enantioselectivity, limiting industrial application. To address these challenges, the authors propose heterologous biosynthesis of DLA in the industrially tractable microorganism Saccharomyces cerevisiae, enabling controlled product profiles and robust fermentation. They report complete pathway reconstitution and DLA production in engineered yeast, achieving titers up to 1.7 mg L−1 at bioreactor scale, demonstrating feasibility of producing ergoline-derived compounds from sugar in a yeast chassis.

Prior approaches to DLA production include: (1) fungal fermentation with ergot-producing filamentous fungi (notably Claviceps purpurea), which yields diverse ergot alkaloid profiles that complicate purification and are vulnerable to strain instability over time; and (2) chemical total syntheses requiring many steps (up to 19) with harsh conditions, low overall yields (only a fraction of 12%), and in some cases enantioselectivity issues even in shorter (8-step) routes with ~10.6% yield. Early and late steps of ergot biosynthesis have been biochemically characterized in native producers, but several enzymes (e.g., EasE, EasD, ClaD/CloA) often prove refractory to expression in heterologous systems, motivating ortholog mining and enzyme screening strategies (e.g., via EFI-EST and sequence similarity networks) to identify functional replacements that operate in yeast.

• Pathway mapping and target selection: The complete DLA biosynthetic route from L-tryptophan requires eight enzymes (including DmaW, EasF, EasC, EasE, EasD, EasA, EasG, and the cytochrome P450 oxidase CloA). Early steps to chanoclavine-I aldehyde are common to ergot alkaloids; later steps direct diversification towards ergoline derivatives. The team focused on identifying orthologs of enzymes reported to be difficult to express heterologously.
• Enzyme ortholog mining: Using the Enzyme Function Initiative-Zyme Similarity Tool and sequence similarity networks, the authors identified and clustered candidate orthologs for EasE and CloA. Putative functional clusters around known active orthologs (e.g., EasE from Aspergillus japonicus) were used to select sequences for screening.
• Yeast screening strains and assays: A yeast platform strain (e.g., YMC17) was constructed with early pathway genes (dmaW, easF, easC) integrated into the genome. Episomal plasmids expressing candidate orthologs were introduced for functional screening. LC-MS/MS assays monitored key intermediates: chanoclavine-I ([M+H]+=257→226 m/z), agroclavine ([M+H]+=239→208 m/z), and DLA ([M+H]+=269→223 m/z). MS/MS spectra and retention time comparisons with standards confirmed product identities.
• EasE screening: Multiple EasE orthologs were expressed in the screening strain to assess production of chanoclavine-I. EasE_Aj and EasE_Ec showed notable activity based on extracted ion chromatograms and MS/MS transitions.
• EasA screening: Orthologs of EasA were expressed in a strain containing early pathway genes plus easD. All selected orthologs produced a compound co-eluting with an agroclavine standard. EasA_Ec, EasA_Cp, and EasA_Nl produced ~2.8–3.1 µg L−1 agroclavine, while EasA_Pi produced ~7-fold less.
• CloA screening: From an SSN built around CloA (e.g., from J. purpurea/C. purpurea), 15 orthologs were screened in yeast for oxidation of agroclavine to DLA. Five orthologs produced a [M+H]+=269 m/z compound co-eluting with a DLA standard and with identical MS/MS spectra, confirming DLA. The C. purpurea ortholog was selected for pathway construction owing to robust and less variable titers in an agroclavine-producing host context.
• Pathway assembly in yeast: A prototype DLA-producing strain was constructed using a modified YeastFab/Golden Gate pipeline. Design principles included stronger promoters for weaker enzymes (e.g., easE), multiple gene copies under weaker promoters to reduce burden, and co-expression of yeast genes (e.g., FAID1/FAID) to enhance protein folding and FAD cofactor availability. The pathway was assembled stepwise in four segments to allow intermediate verification by LC-MS/MS.
• Cultivation and scale-up: Small-scale shake-flask cultures were grown in synthetic complete media with glucose/galactose induction and analyzed by LC-MS/MS. For bioreactor production, a fed-batch strategy in 1 L and 4 L vessels used SC-URA media with 50 mM ammonium-succinate (pH 5.8), controlled induction/feeding phases (I–III) with galactose for induction, and DO control with variable stirring and aeration. Samples were analyzed by standard addition on LC-MS to quantify DLA. NMR analysis was performed on pooled extracts from 8 L shake-flask scale-up to further validate DLA structure.
• Analytical methods: LC-MS/MS (Agilent Q-TOF) with C18 chromatography and defined gradients; transitions monitored included 239→208 m/z for agroclavine and 269→223 m/z for DLA. Product identities were confirmed by retention time and MS/MS spectra versus standards; isotope tracing with 13C-tryptophan showed expected +1/z shifts in fragment ions, indicating biosynthesis from tryptophan.
• Data analysis: Standard curves and linear regression (GraphPad Prism) were used for quantification; results reported as means ± standard deviation from biological replicates.

• Complete reconstitution of the D-lysergic acid (DLA) biosynthetic pathway from L-tryptophan in Saccharomyces cerevisiae was achieved using selected orthologs for difficult-to-express enzymes and a modular assembly strategy.
• Identification of functional enzyme orthologs in yeast: • EasE: EasE_Aj and EasE_Ec showed robust production of chanoclavine-I (257→226 m/z). • EasA: Multiple orthologs produced agroclavine, with EasA_Ec, EasA_Cp, and EasA_Nl yielding ~2.8–3.1 µg L−1; EasA_Pi produced ~7-fold less. No undesired alternative products were detected among the tested orthologs. • CloA: Five CloA orthologs produced a DLA-identical compound ([M+H]+=269 m/z) by LC-MS/MS; the C. purpurea ortholog was selected for pathway construction due to consistent DLA titers.
• Production titers: • Bioreactors (fed-batch): Maximum DLA titers of 1.7 mg L−1 (1 L) and 1.4 mg L−1 (4 L) with cell mass ~26–29 g L−1 under controlled feeding and pH (5.8) conditions. • Intermediates and final product identities were confirmed by co-elution with standards, MS/MS fragmentation matches, and NMR (from 8 L shake-flask scale-up extract). Isotopic labeling supported biosynthesis from tryptophan.
• Process design elements contributing to function included tailored promoter strengths, multiple gene copies to balance burden, and co-expression of folding/cofactor biosynthesis genes (e.g., FAID) to support FAD-dependent EasE activity.
• The engineered yeast produced DLA directly from central metabolism-derived tryptophan or media tryptophan, demonstrating a functional de novo biosynthetic route from sugar feedstock.

This study addresses the long-standing challenges of DLA manufacture—heterogeneous product mixtures from filamentous fungi and low-yield, non-enantioselective chemical syntheses—by demonstrating a fully heterologous biosynthetic route to DLA in S. cerevisiae. Strategic selection of enzyme orthologs overcame prior expression bottlenecks (notably EasE and CloA) and enabled the assembly of a controllable, modular pathway. LC-MS/MS and NMR analyses verify that the engineered pathway produces authentic DLA, while isotopic labeling confirms utilization of tryptophan derived from yeast metabolism. Achieving mg L−1 titers at liter-scale fermentations provides a proof-of-concept foundation for future process intensification. Importantly, a yeast platform constrains the product profile to targeted ergoline derivatives, simplifying downstream processing relative to native ergot fungi. These findings open routes to produce DLA and potentially tailor ergoline scaffolds via enzyme swaps and late-stage diversification, aligning with interests in neurological and psychiatric therapeutics, including renewed investigations into psychedelic-derived medicines. While current titers are below commercial needs, the study establishes key enzymatic and genetic components and demonstrates scalability principles necessary for subsequent optimization.

The authors reconstituted the complete biosynthetic pathway to D-lysergic acid in baker’s yeast, identified and validated functional orthologs for critical pathway enzymes, and assembled a modular yeast strain capable of producing DLA from sugar-derived metabolism. The engineered strains achieved up to 1.7 mg L−1 DLA in 1 L fed-batch fermentations and 1.4 mg L−1 in 4 L, with product identities confirmed by LC-MS/MS and NMR. This work provides a tractable microbial platform for ergoline biosynthesis that can be leveraged for discovery and production of natural and semi-synthetic derivatives with therapeutic potential. Future work should focus on: (i) relieving pathway bottlenecks via enzyme engineering and expression tuning; (ii) optimizing cofactor supply and folding chaperones; (iii) host strain and bioprocess optimization (e.g., carbon feeding strategies, oxygen transfer, pH control) to raise titers; and (iv) expanding pathway branches to access diverse ergoline derivatives for medicinal chemistry.

• Production titers remain in the mg L−1 range, well below levels required for commercial viability; substantial strain and bioprocess optimization are needed.
• Some sections of the pathway, particularly the two-step oxidation by CloA, remain mechanistically undercharacterized, limiting rational optimization.
• Enzyme ortholog performance exhibited variability; broader screening and protein engineering may be necessary to ensure robustness across scales and conditions.
• The study focuses on a single host chassis and induction regime; alternative hosts or expression systems might further improve yields but were not explored here.
• Downstream processing and purification at scale were not demonstrated; economic and process feasibility remain to be established.