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

Hiroyuki Morita, Kiyofumi Wanibuchi, Hirohiko Nii, Ryohei Kato, Shigetoshi Sugio, Ikuro Abe and Rodney B. Croteau
Proceedings of the National Academy of Sciences of the United States of America
Vol. 107, No. 46 (November 16, 2010), pp. 19778-19783
Stable URL: http://www.jstor.org/stable/25748756
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Structural basis for the one-pot formation of the diarylheptanoid
              scaffold by curcuminoid synthase from Oryza sativa
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Abstract

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.

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