Structural basis for biosynthetic programming of fungal aromatic polyketide cyclization

Area of Science:

• Biochemistry
• Molecular Biology
• Natural Product Synthesis

Background:

• Polyketides are natural products with varied structures and bioactivities.
• Fungal iterative polyketide synthases (IPKSs) produce aromatic compounds through complex cyclizations.
• The mechanisms controlling polyketide cyclization specificity have remained largely unknown.

Purpose of the Study:

• To determine the structure and mechanism of the Product Template (PT) domain in NR-PKSs.
• To understand how PT domains control polyketide cyclization and aromatization.
• To provide insights into the biosynthesis of aflatoxin B1.

Main Methods:

• X-ray crystallography of a dissected PT monodomain from PksA.
• Co-crystallization with substrate mimics (palmitate, bicyclic analog).
• Site-directed mutagenesis and molecular docking studies.

Main Results:

• The PT domain adopts a novel 'double hot dog' (DHD) fold.
• PT binds both linear and bicyclic polyketide precursors.
• Key residues for substrate binding, catalysis, and a unique binding pocket were identified.

Conclusions:

• The DHD fold and active site of PT domains are conserved across IPKSs.
• Mechanistic insights into PT function are generalizable for NR-PKS cyclization control.
• This study lays the groundwork for understanding and engineering NR-PKS specificity.