G2 Helix as the Plastic Region Modulating Diastereoselectivity of Cyclization in Fungal Bifunctional Sesterterpene Synthases
Bibliographic record
Abstract
Sesterterpenoids are a rare class of terpenes with potential pharmaceutical applications. To date, most of the currently characterized fungal sesterterpenoids are produced through the catalysis of bifunctional sesterterpene synthases (BF-STPSs). However, the full catalytic potential of BF-STPSs is not yet fully understood. Here, using site-directed mutagenesis and computational simulations, we identified the G2 helix of BF-STPSs as a structurally plastic region that governs divergent cyclization pathways, leading to the formation of unique terpenes with distinct diastereoselectivity. Mutations in the functional site residues of the G2 helix in Type A BF-STPSs, DpPS and FoFS, altered the conformational flexibility of the carbocation intermediates, yielding a series of previously uncharacterized sesterterpenes with unprecedented diastereoselectivity in B-ring cyclization via a selective attack on the diastereotopic faces of the olefin. Notably, FoFS-V195A catalyzed the formation of five different skeleton types, while DpPS-V194A represented a rare example of a protein-engineered switch from a bicyclic to a tricyclic skeleton with a Z -configured Δ 11,12 double bond. Density functional theory (DFT) calculations and molecular dynamics (MD) simulations provided further insights into the reaction details and active site dynamics. These findings highlight key amino acids within the G2 helix of BF-STPSs as mutational hotspots, providing an efficient strategy to accelerate the discovery of structurally diverse sesterterpenes.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".