Skip Navigation
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Your Environment. Your Health.

Publication Detail

Title: Structure and function of an iterative polyketide synthase thioesterase domain catalyzing Claisen cyclization in aflatoxin biosynthesis.

Authors: Korman, Tyler Paz; Crawford, Jason M; Labonte, Jason W; Newman, Adam G; Wong, Justin; Townsend, Craig A; Tsai, Shiou-Chuan

Published In Proc Natl Acad Sci U S A, (2010 Apr 06)

Abstract: Polyketide natural products possess diverse architectures and biological functions and share a subset of biosynthetic steps with fatty acid synthesis. The final transformation catalyzed by both polyketide synthases (PKSs) and fatty acid synthases is most often carried out by a thioesterase (TE). The synthetic versatility of TE domains in fungal nonreducing, iterative PKSs (NR-PKSs) has been shown to extend to Claisen cyclase (CLC) chemistry by catalyzing C-C ring closure reactions as opposed to thioester hydrolysis or O-C/N-C macrocyclization observed in previously reported TE structures. Catalysis of C-C bond formation as a product release mechanism dramatically expands the synthetic potential of PKSs, but how this activity was acquired has remained a mystery. We report the biochemical and structural analyses of the TE/CLC domain in polyketide synthase A, the multidomain PKS central to the biosynthesis of aflatoxin B(1), a potent environmental carcinogen. Mutagenesis experiments confirm the predicted identity of the catalytic triad and its role in catalyzing the final Claisen-type cyclization to the aflatoxin precursor, norsolorinic acid anthrone. The 1.7 A crystal structure displays an alpha/beta-hydrolase fold in the catalytic closed form with a distinct hydrophobic substrate-binding chamber. We propose that a key rotation of the substrate side chain coupled to a protein conformational change from the open to closed form spatially governs substrate positioning and C-C cyclization. The biochemical studies, the 1.7 A crystal structure of the TE/CLC domain, and intermediate modeling afford the first mechanistic insights into this widely distributed C-C bond-forming class of TEs.

PubMed ID: 20332208 Exiting the NIEHS site

MeSH Terms: Aflatoxins/biosynthesis*; Biocatalysis; Crystallography, X-Ray; Cyclization; Fungal Proteins/chemistry*; Fungal Proteins/metabolism*; Hydrophobic and Hydrophilic Interactions; Mutation; Polyketide Synthases/chemistry*; Polyketide Synthases/genetics; Polyketide Synthases/metabolism*; Protein Folding; Protein Structure, Tertiary; Thiolester Hydrolases/chemistry*; Thiolester Hydrolases/metabolism*

Back
to Top