A specific cytochrome P450 hydroxylase in herboxidiene biosynthesis

Area of Science:

• Biochemistry
• Natural Product Biosynthesis
• Enzymology

Background:

• Herboxidiene is an anti-cholesterol natural product synthesized by Streptomyces chromofuscus A7847.
• Its biosynthesis involves a modular polyketide synthase and three tailoring enzymes, including the putative monooxygenase HerG.

Purpose of the Study:

• To biochemically characterize the putative monooxygenase HerG involved in herboxidiene biosynthesis.
• To elucidate the specific role of HerG in the herboxidiene pathway.

Main Methods:

• Expression of HerG in Escherichia coli and purification of the enzyme.
• Biochemical studies including substrate specificity and kinetic analysis (kcat/Km).
• In vitro co-reaction of HerG with HerF and analysis of product formation in S. chromofuscus.

Main Results:

• HerG was identified as a cytochrome P450 enzyme catalyzing stereospecific C-18 hydroxylation.
• HerG exhibits high substrate specificity, efficiently hydroxylating 18-deoxy-25-demethyl-herboxidiene but not 18-deoxy-herboxidiene.
• The kcat/Km value for HerG-catalyzed hydroxylation was determined to be 1669.70±47.36 M(-1) s(-1).
• HerG and HerF work sequentially to convert 18-deoxy-25-demethyl-herboxidiene to herboxidiene, with 18-deoxy-herboxidiene as a byproduct.

Conclusions:

• HerG is a key cytochrome P450 enzyme in the herboxidiene biosynthetic pathway, responsible for a critical hydroxylation step.
• The sequential action of HerG and HerF leads to the formation of herboxidiene from its precursor.
• Understanding this pathway provides insights into the biosynthesis of natural products with potential pharmaceutical applications.