Vinylogous chain branching catalysed by a dedicated polyketide synthase module.

Area of Science:

• Biochemistry
• Molecular Biology
• Synthetic Biology

Background:

• Modular polyketide synthases (PKSs) are crucial for producing complex polyketides, many serving as leads for anti-infective and anti-tumoral drugs.
• Current PKS research primarily focuses on linear backbone assembly, limiting structural diversity in polyketide compounds.
• Rational engineering of PKS pathways is essential for generating novel drug analogues.

Purpose of the Study:

• To investigate a novel PKS module from Burkholderia rhizoxinica with a unique chain branching capability.
• To elucidate the mechanism of this non-canonical polyketide assembly and its structural basis.
• To explore the implications of this discovery for generating structural diversity in polyketides.

Main Methods:

• In vitro reconstitution of the PKS module.
• X-ray crystallography of key domains.
• Site-directed mutagenesis experiments.
• Analysis of intermediate states.

Main Results:

• A new PKS module capable of Michael-type acetyl addition, creating a branch in the polyketide chain, was identified.
• The ketosynthase domain was identified as critical for this branching activity.
• A covalently linked intermediate state revealed a novel mechanism for chain alkylation, distinct from terpenoid-like branching.
• This non-canonical modification is essential for the bioactivity of rhizoxin, a potent anti-mitotic agent.

Conclusions:

• The study unveils a new PKS module and mechanism, expanding the biosynthetic scope of polyketide assembly.
• This discovery provides a foundation for rationally engineering PKS pathways to create novel polyketide structures with therapeutic potential.
• The proposed vinylogous branching reaction offers a unifying model for PKS modules with a ketosynthase-branching-acyl-carrier-protein architecture.