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J Biol Chem. 2006 Sep 15;281(37):27557-65. Epub 2006 Jun 9.

Structural basis for the redox control of plant glutamate cysteine ligase.

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1
Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.

Abstract

Glutathione (GSH) plays a crucial role in plant metabolism and stress response. The rate-limiting step in the biosynthesis of GSH is catalyzed by glutamate cysteine ligase (GCL) the activity of which is tightly regulated. The regulation of plant GCLs is poorly understood. The crystal structure of substrate-bound GCL from Brassica juncea at 2.1-A resolution reveals a plant-unique regulatory mechanism based on two intramolecular redox-sensitive disulfide bonds. Reduction of one disulfide bond allows a beta-hairpin motif to shield the active site of B. juncea GCL, thereby preventing the access of substrates. Reduction of the second disulfide bond reversibly controls dimer to monomer transition of B. juncea GCL that is associated with a significant inactivation of the enzyme. These regulatory events provide a molecular link between high GSH levels in the plant cell and associated down-regulation of its biosynthesis. Furthermore, known mutations in the Arabidopsis GCL gene affect residues in the close proximity of the active site and thus explain the decreased GSH levels in mutant plants. In particular, the mutation in rax1-1 plants causes impaired binding of cysteine.

PMID:
16766527
DOI:
10.1074/jbc.M602770200
[Indexed for MEDLINE]
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