Assembly-Line Catalysis in Bifunctional Terpene Synthases.

Area of Science:

• Biochemistry and Organic Chemistry
• Enzymology and Natural Product Biosynthesis
• Structural Biology and Protein Engineering

Background:

• Terpenoid natural products, exceeding 95,000 identified, are primarily synthesized by terpene synthases.
• These enzymes, including prenyltransferases and cyclases, build complex hydrocarbon structures from simple isoprenoid units.
• Terpene cyclization reactions are intricate, involving carbocation intermediates and diverse protein folds (α, β, γ).

Purpose of the Study:

• To review structure-function relationships of bifunctional terpene synthases, focusing on oligomeric systems.
• To explore how protein domain architectures (α, αβ, αβγ, βγ, β) dictate catalytic mechanisms.
• To highlight the potential of these systems in synthetic biology for high-value terpenoid production.

Main Methods:

• Analysis of crystal structures of various terpene synthase domain architectures.
• Investigation of bifunctional enzymes catalyzing sequential biosynthetic steps.
• Focus on oligomeric complexes, including fungal (+)-copalyl diphosphate synthase and fusicoccadiene synthase.

Main Results:

• Class I cyclases (α domain) use metal clusters, while Class II cyclases (β domain) use protonation for carbocation formation.
• Bifunctional synthases can combine domains (e.g., αα, αβγ) for assembly line catalysis.
• Oligomeric complexes, like fungal synthases, exhibit substrate channeling and efficient carbon management.

Conclusions:

• Protein domain organization dictates terpene synthase function and substrate specificity.
• Oligomeric assembly line catalysis by bifunctional terpene synthases offers high efficiency.
• These systems present promising platforms for synthetic biology applications in terpenoid production.