Decrypting the programming of β-methylation in virginiamycin M biosynthesis.

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Trans-AT polyketide synthases (PKS) expand polyketide diversity through β-branching.
• 3-hydroxy-3-methylglutaryl synthase enzyme cassettes catalyze these multi-step transformations.
• Mechanisms of β-branching are known, but substrate selection remains unclear.

Purpose of the Study:

• To identify the basis for substrate selection in module 5 of the virginiamycin M trans-AT PKS.
• To investigate potential additional sites for β-methylation within the PKS pathway.

Main Methods:

• Integrative structural biology was employed to analyze substrate recognition.
• High-performance liquid chromatography-mass spectrometry (HPLC-MS) coupled with isotopic labeling and pathway inactivation was used.
• In vitro assays were performed to assess enzyme activity.

Main Results:

• The structural basis for substrate choice in module 5 of the virginiamycin M trans-AT PKS was identified.
• Module 7 was confirmed as a site for β-methylation.
• A metabolite with a second β-methyl group was detected, confirming additional branching.

Conclusions:

• Multiple control mechanisms coordinate to regulate β-branching in polyketide biosynthesis.
• Variations in these controls can be exploited to generate novel polyketide derivatives.