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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

The Crystal Structures of Zea mays and Arabidopsis 4-Hydroxyphenylpyruvate Dioxygenase

Max-Planck-Institut für Biochemie, Abteilung für Strukturforschung, 82152 Martinsried, Germany

The transformation of 4-hydroxyphenylpyruvate to homogentisate, catalyzed by 4-hydroxyphenylpyruvate dioxygenase (HPPD), plays an important role in degrading aromatic amino acids. As the reaction product homogentisate serves as aromatic precursor for prenylquinone synthesis in plants, the enzyme is an interesting target for herbicides. In this study we report the first x-ray structures of the plant HPPDs of Zea mays and Arabidopsis in their substrate-free form at 2.0 Å and 3.0 Å resolution, respectively. Previous biochemical characterizations have demonstrated that eukaryotic enzymes behave as homodimers in contrast to prokaryotic HPPDs, which are homotetramers. Plant and bacterial enzymes share the overall fold but use orthogonal surfaces for oligomerization. In addition, comparison of both structures provides direct evidence that the C-terminal helix gates substrate access to the active site around a nonheme ferrous iron center. In the Z. mays HPPD structure this helix packs into the active site, sequestering it completely from the solvent. In contrast, in the Arabidopsis structure this helix tilted by about 60° into the solvent and leaves the active site fully accessible. By elucidating the structure of plant HPPD enzymes we aim to provide a structural basis for the development of new herbicides.

² Bayer CropScience, BCS-R-TR, Building 6240, Alfred-Nobel-Str. 50, 40789 Monheim, Germany.

³ Present address: Antisense Pharma GmbH, Josef-Engert-Str. 9, 93053 Regensburg, Germany.

⁴ Present address: Division of Chemistry and Chemical Engineering, California Institute of Technology, Mail Code 114–96, Pasadena, CA 91125.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.103.034082.

^* Corresponding author; fritze{at}biochem.mpg.de; fax +49–(89)–8578–3516.

Received September 29, 2003; returned for revision December 22, 2003; accepted December 22, 2003.

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