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Refined crystal structure of ascorbate oxidase at 1.9 A resolution
A Messerschmidt1, R Ladenstein, R Huber
1Max-Planck-Institut für Biochemie, Martinsried, F.R.G.
Journal of Molecular Biology
|March 5, 1992
Summary
The crystal structure of Zucchini ascorbate oxidase reveals a tetrameric arrangement with three beta-barrel domains per subunit. This enzyme contains four copper atoms, including type-1, type-2, and type-3 copper centers, crucial for its function.
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Ascorbate oxidase (EC 1.10.3.3) is a multi-copper enzyme involved in plant defense and cell wall metabolism.
- Understanding its structure is key to elucidating its catalytic mechanism and substrate interactions.
Purpose of the Study:
- To determine the high-resolution crystal structure of fully oxidized ascorbate oxidase from Zucchini.
- To analyze the arrangement of copper atoms and protein domains within the enzyme structure.
Main Methods:
- Energy-restrained least-squares refinement of X-ray crystallographic data to 1.90 A resolution.
- Analysis of protein atoms, copper coordination, solvent molecules, and symmetry in the tetrameric structure.
Main Results:
- The refined structure reveals a tetrameric assembly with D2 symmetry, each subunit composed of three beta-barrel domains.
- Four copper atoms per subunit are identified: a type-1 copper in domain 3, and a trinuclear cluster (putative type-2 and type-3 coppers) ligated by histidine residues.
- Defined electron density for an N-linked glycosylation site at Asn92.
Conclusions:
- The structural data provides insights into the coordination of copper ions and the overall fold of ascorbate oxidase.
- The proximity of the type-1 copper to a potential substrate binding site is suggested.
- The findings contribute to understanding the structure-function relationship of this important plant enzyme.