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Title: AtGRXcp, an "Arabidopsis" chloroplastic glutaredoxin, is critical for protection against protein oxidative damage

Author
item CHENG, NING-HUI - BAYLOR COLLEGE MED
item LIU, JIAN-ZHONG - SAMUEL ROBERTS NOBLE FOUN
item BROCK, AMANDA - BAYLOR COLLEGE MED
item NELSON, RICHARD - SAMUEL ROBERTS NOBLE FOUN
item Hirschi, Kendal

Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2006
Publication Date: 9/8/2006
Citation: Cheng, N-H., Liu, J-Z., Brock, A., Nelson, R.S., Hirschi, K.D. 2006. AtGRXcp, an "Arabidopsis" chloroplastic glutaredoxin, is critical for protection against protein oxidative damage. Journal of Biological Chemistry. 281(36):26280-26288.

Interpretive Summary: All plant and animal life have to deal with the stress of oxygen. That is, too little or too much and you die! Antioxidant systems deal with this oxygen stress. In this report, we have identified a new type of antioxidant system in plants. We have characterized the way this antioxidant works and how it helps plants deal with biological adaptations to the environment. Hopefully in the future we can use this knowledge to make more robust plants that can grow in a variety of difficult environments.

Technical Abstract: Glutaredoxins (Grxs) are ubiquitous small heat-stable disulfide oxidoreductases and members of the thioredoxin (Trx) fold protein family. In bacterial, yeast, and mammalian cells, Grxs appear to be involved in maintaining cellular redox homeostasis. However, in plants, the physiological roles of Grxs have not been fully characterized. Recently, an emerging subgroup of Grxs with one cysteine residue in the putative active motif (monothiol Grxs) has been identified but not well characterized. Here we demonstrate that a plant protein, AtGRXcp, is a chloroplast-localized monothiol Grx with high similarity to yeast Grx5. In yeast expression assays, AtGRXcp localized to the mitochondria and suppressed the sensitivity of yeast "grx5" cells to H[2]O[2] and protein oxidation. AtGRXcp expression can also suppress iron accumulation and partially rescue the lysine auxotrophy of yeast "grx5" cells. Analysis of the conserved monothiol motif suggests that the cysteine residue affects "AtGRXcp" expression and stability. "In planta, AtGRXcp" expression was elevated in young cotyledons, green tissues, and vascular bundles. Analysis of "atgrxcp" plants demonstrated defects in early seedling growth under oxidative stresses. In addition, "atgrxcp" lines displayed increased protein carbonylation within chloroplasts. Thus, this work describes the initial functional characterization of a plant monothiol Grx and suggests a conserved biological function in protecting cells against protein oxidative damage.