Type II polyketide synthases (PKSs) are protein assemblies, encoded by biosynthetic gene clusters in microorganisms, that manufacture structurally complex and pharmacologically relevant molecules. Acyl carrier proteins (ACPs) play a central role in biosynthesis by shuttling malonyl-based building blocks and polyketide intermediates to catalytic partners for chemical transformations. Because ACPs serve as central hubs in type II PKSs, they can also represent roadblocks to successfully engineering synthases capable of manufacturing ‘unnatural natural products.’ Therefore, understanding ACP conformational dynamics and protein interactions is essential to enable the strategic redesign of type II PKSs. However, the inherent flexibility and transience of ACP interactions pose challenges to gaining insight into ACP structure and function. In this review, we summarize how the application of chemical probes and molecular dynamic simulations has increased our understanding of the structure and function of type II PKS ACPs. We also share how integrating these advances in type II PKS ACP research with newfound access to key enzyme partners, such as the ketosynthase-chain length factor, sets the stage to unlock new biosynthetic potential.
Microbial type II polyketides serve as powerful medicinally relevant agents. These molecules are biosynthesized by polyketide synthases (PKSs) comprised of a core ketosynthase-chain length factor (KS-CLF) and phosphopantetheinylated acyl carrier protein (holo-ACP). While engineering type II PKSs holds potential to unlock sustainable access to diverse bioactive molecules, the inability to obtain cognate type II KS-CLFs andholo-ACPs forin vitrostudies represents a longstanding barrier. Herein, we share how the sequence and structural analysis of theGloeocapsa sp.PCC 7428 ACP allowed us to tune to a requisite weak yet specific interaction with a phosphopantetheinyl transferase to afford theholo-ACP. This, coupled with our ability to heterologously express the cognate KS-CLF in high quantities, unlocked access to polyketide products viain vitromultienzyme assembly. We hope this work inspires future studies of type II PKSs that have previously evaded heterologous expression or have yet to be explored.Abstract Figure
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