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Insight into a natural Diels–Alder reaction from the structure of macrophomate synthase


The Diels–Alder reaction, which forms a six-membered ring from an alkene (dienophile) and a 1,3-diene, is synthetically very useful for construction of cyclic products with high regio- and stereoselectivity under mild conditions1. It has been applied to the synthesis of complex pharmaceutical and biologically active compounds2. Although evidence3,4,5,6,7 on natural Diels–Alderases has been accumulated in the biosynthesis of secondary metabolites8, there has been no report on the structural details of the natural Diels–Alderases. The function and catalytic mechanism of the natural Diels–Alderase are of great interest owing to the diversity of molecular skeletons in natural Diels–Alder adducts8. Here we present the 1.70 Å resolution crystal structure of the natural Diels–Alderase, fungal macrophomate synthase (MPS)3, in complex with pyruvate. The active site of the enzyme is large and hydrophobic, contributing amino acid residues that can hydrogen-bond to the substrate 2-pyrone. These data provide information on the catalytic mechanism of MPS, and suggest that the reaction proceeds via a large-scale structural reorganization of the product.

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Figure 1: Details of individual reaction steps with macrophomate synthase.
Figure 2: Overall structure of MPS.
Figure 3: Active site view showing Mg2+ coordination, the electron density map, and the proposed model of the early transition state.
Figure 4: Comparison of Diels–Alderases.


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We thank S. Wakatsuki, M. Suzuki and N. Igarashi of the Photon Factory, Japan, for help in data collection at beamline BL18B. This work was supported in part by National Project on Protein Structural and Functional Analyses from the Ministry of Education, Science, Sports and Culture of Japan.

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Correspondence to Hideaki Oikawa or Isao Tanaka.

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Ose, T., Watanabe, K., Mie, T. et al. Insight into a natural Diels–Alder reaction from the structure of macrophomate synthase. Nature 422, 185–189 (2003).

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