Structural basis for the one-pot formation of the diarylheptanoid scaffold by curcuminoid synthase from Oryza sativa

Curcuminoid synthase (CUS) from Oryza sativa is a plant-specific type III polyketide synthase (PKS) that catalyzes the remarkable one-pot formation of the C₆-C₇-C₆ diarylheptanoid scaffold of bisdemethoxycurcumin, by the condensation of two molecules of 4-coumaroyl-CoA and one molecule of malonyl-Co...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2010-11, Vol.107 (46), p.19778-19783
Main Authors: Morita, Hiroyuki, Wanibuchi, Kiyofumi, Nii, Hirohiko, Kato, Ryohei, Sugio, Shigetoshi, Abe, Ikuro, Croteau, Rodney B.
Format: Article
Language:English
Subjects:
Binding sites
Biochemistry - methods
Biological Sciences
Catalytic Domain
Chalconoids
Chromatography, High Pressure Liquid
Condensation
Crystal structure
Crystallography, X-Ray
Diarylheptanoids - chemistry
Diarylheptanoids - metabolism
Electrons
Enzymes
Hydrogen Bonding
Hydrogen bonds
Ligases - chemistry
Ligases - metabolism
Models, Molecular
Molecular structure
Molecules
Monomers
Mutagenesis - genetics
Mutation
Oryza - enzymology
Polyketides
Rice
Scaffolds
Structure-Activity Relationship
Substrate specificity
Thiolester Hydrolases - chemistry
Thiolester Hydrolases - metabolism
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Summary:Curcuminoid synthase (CUS) from Oryza sativa is a plant-specific type III polyketide synthase (PKS) that catalyzes the remarkable one-pot formation of the C₆-C₇-C₆ diarylheptanoid scaffold of bisdemethoxycurcumin, by the condensation of two molecules of 4-coumaroyl-CoA and one molecule of malonyl-CoA. The crystal structure of O. sativa CUS was solved at 2.5-Å resolution, which revealed a unique, downward expanding active-site architecture, previously unidentified in the known type III PKSs. The large active-site cavity is long enough to accommodate the two C₆-C₃ coumaroyl units and one malonyl unit. Furthermore, the crystal structure indicated the presence of a putative nucleophilic water molecule, which forms hydrogen bond networks with Ser351-Asn142-H₂O-Tyr207-Glu202, neighboring the catalytic Cys174 at the active-site center. These observations suggest that CUS employs unique catalytic machinery for the one-pot formation of the C₆-C₇-C₆ scaffold. Thus, CUS utilizes the nucleophilic water to terminate the initial polyketide chain elongation at the diketide stage. Thioester bond cleavage of the enzyme-bound intermediate generates 4-coumaroyldiketide acid, which is then kept within the downward expanding pocket for subsequent decarboxylative condensation with the second 4-coumaroyl-CoA starter, to produce bisdemethoxycurcumin. The structure-based site-directed mutants, M265L and G274F, altered the substrate and product specificities to accept 4-hydroxyphenylpropionyl-CoA as the starter to produce tetrahydrobisdemethoxycurcumin. These findings not only provide a structural basis for the catalytic machinery of CUS but also suggest further strategies toward expanding the biosynthetic repertoire of the type III PKS enzymes.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1011499107