Iterative chain elongation by a pikromycin monomodular polyketide synthase

Area of Science:

• Biochemistry
• Molecular Biology
• Organic Chemistry

Background:

• The pikromycin polyketide synthase (Pik PKS) is known for producing macrolactones.
• Understanding polyketide synthesis mechanisms, particularly chain extension, is crucial.

Purpose of the Study:

• To investigate the mechanistic details of the chain extension process in polyketide synthesis.
• To explore the function of PikAIII and PikAIV in generating triketide lactones.

Main Methods:

• Overexpression and purification of PikAIII and PikAIV proteins.
• Incubation of purified proteins with (14)C-methylmalonyl-CoA as the sole substrate.
• Analysis of triketide lactone product formation.

Main Results:

• PikAIII and PikAIV proteins were successfully overexpressed and purified.
• Both proteins demonstrated the ability to generate triketide lactone products using methylmalonyl-CoA.
• Monomodular PikAIII produced TKL (1) alone, and TKL (2) in combination with PikAIV.
• Product formation was dependent on enzymatic decarboxylation and acyl chain transfer within the enzyme.

Conclusions:

• The synthesis of TKL (1) by PikAIII likely involves iterative triketide chain assembly within a PikAIII homodimer.
• This process is analogous to nonmodular type I PKS systems.
• The study provides insights into the fundamental mechanisms of polyketide synthesis.