Structure of a modular polyketide synthase reducing region

The chemical scaffolds of numerous therapeutics are polyketide natural products, many formed by bacterial modular polyketide synthases (PKS). The large and flexible dimeric PKS modules have distinct extension and reducing regions. Structures are known for all individual enzyme domains and several extension regions. Here, we report the structure of the full reducing region from a modular PKS, the ketoreductase (KR), dehydratase (DH), and enoylreductase (ER) domains of module 5 of the juvenimicin PKS. The modular PKS-reducing region has a different architecture than the homologous fatty acid synthase (FAS) and iterative PKS systems in its arrangement of domains and dimer interface. The structure reveals a critical role for linker peptides in the domain interfaces, leading to discovery of key differences in KR domains dependent on module composition. Finally, our studies provide insight into the mechanism underlying modular PKS intermediate shuttling by carrier protein (ACP) domains. [Display omitted] •Modular polyketide synthase reducing regions diverge from iterative megasynthases•Interdomain linkers form “hydrophobic glue” in domain interfaces•KR domains vary depending on the presence or absence of same-module DH domains•Fully reducing PKS modules may function asynchronously McCullough et al. characterize the architecture of JuvEIII DH-ER-KR, the fully reducing region of module 5 in the juvenimicin polyketide synthase. The structure illustrates the divergence of modular PKS from iterative megasynthase homologs including metazoan fatty acid synthase and reveals structural elements common to PKS modules with fully reducing tridomains.