Structural determinants of reductive terpene cyclization in iridoid biosynthesis

Area of Science:

• Biochemistry
• Enzymology
• Organic Chemistry

Background:

• Iridoid monoterpenes are vital natural products with significant ecological and pharmacological roles.
• Their biosynthesis involves a unique reductive cyclization pathway distinct from typical terpene cyclizations.

Purpose of the Study:

• To determine the crystal structure of iridoid cyclase from Catharanthus roseus.
• To elucidate the enzyme's substrate binding and catalytic mechanism using a mechanism-inspired inhibitor.
• To differentiate iridoid synthase from its homolog, progesterone 5β-reductase.

Main Methods:

• X-ray crystallography to obtain the enzyme-inhibitor complex structure.
• Biochemical assays to study enzyme kinetics and function.
• Comparative analysis with homologous enzymes.

Main Results:

• The crystal structure reveals key features of iridoid cyclase's active site and substrate interaction.
• The study illuminates the unique catalytic mechanism distinguishing it from canonical terpene cyclases.
• Significant differences between iridoid synthase and progesterone 5β-reductase were identified.

Conclusions:

• The structure provides a detailed understanding of iridoid monoterpene biosynthesis.
• This work offers a foundation for engineering iridoid cyclases for biotechnological applications.
• The findings enhance our knowledge of enzyme evolution and function.