3ILS

The Thioesterase Domain from PksA

Summary for 3ILS

• Entry DOI: 10.2210/pdb3ils/pdb
• Descriptor: Aflatoxin biosynthesis polyketide synthase (2 entities in total)
• Functional Keywords: a/b hydrolase, thioesterase, norsolorinic acid, aflatoxin, pksa, polyketide, acyltransferase, multifunctional enzyme, phosphopantetheine, hydrolase
• Biological source: Aspergillus parasiticus
• Total number of polymer chains: 1
• Total formula weight: 29167.55

Authors

Korman, T.P. (deposition date: 2009-08-07, release date: 2010-04-07, Last modification date: 2024-02-21)

Primary citation

Korman, T.P.,Crawford, J.M.,Labonte, J.W.,Newman, A.G.,Wong, J.,Townsend, C.A.,Tsai, S.C.
Structure and function of an iterative polyketide synthase thioesterase domain catalyzing Claisen cyclization in aflatoxin biosynthesis.
Proc.Natl.Acad.Sci.USA, 107:6246-6251, 2010

PubMed 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: 20332208
DOI: 10.1073/pnas.0913531107

Experimental method

X-RAY DIFFRACTION (1.7 Å)