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Exploring a Unique Class II Diterpene Cyclase: The Modified Catalytic Acid Motif Contributes to Ring Contraction in
Kristin Helwig1, Jun Xie2, Cody Lemke1
1Roy J. Carver Department of Biochemistry, Biophysics & Molecular Biology, Iowa State University, Ames, Iowa 50011, United States.
Organic Letters
|January 21, 2026
Summary
Class II diterpene cyclase uses a unique DxDM motif to produce mutildienyl pyrophosphate (MPP). Mutating this motif blocks MPP production and yields a novel hydroxylated product, revealing insights into diterpene biosynthesis.
Area of Science:
- Biochemistry
- Organic Chemistry
- Enzymology
Background:
- Pleuromutilin biosynthesis involves class II diterpene cyclases.
- These enzymes typically possess a conserved DxDD motif crucial for catalysis.
- The pleuromutilin enzyme exhibits a unique DxDM variant.
Purpose of the Study:
- To investigate the role of the unique DxDM motif in class II diterpene cyclase activity.
- To understand the mechanism behind the "A" ring contracted product, mutildienyl pyrophosphate (MPP).
Main Methods:
- Site-directed mutagenesis was used to substitute aspartate for methionine in the DxDM motif.
- The catalytic activity of the wild-type and mutant enzymes was analyzed.
- Products of the enzymatic reactions were identified and characterized.
Main Results:
- The DxDM to DxDD mutation significantly inhibited the production of mutildienyl pyrophosphate (MPP).
- A novel hydroxylated product, syn-halima-13E-en-5β-ol-15-PP, was formed in the mutant enzyme reactions.
- This suggests the methionine residue plays a critical role in MPP formation.
Conclusions:
- The unique DxDM motif is essential for the formation of the "A" ring contracted product, MPP.
- The substitution of methionine alters the enzyme's catalytic pathway, leading to a different product.
- This study provides key insights into the mechanism of this unique diterpene cyclase.
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