title: Copper chaperone antioxidant protein1 is essential for copper homeostasis.
abstract: Copper (Cu) is essential for plant growth but toxic in excess. Specific molecular mechanisms maintain Cu homeostasis to facilitate its use and avoid the toxicity. Cu chaperones, proteins containing a Cu-binding domain(s), are thought to assist Cu intracellular homeostasis by their Cu-chelating ability. In Arabidopsis (Arabidopsis thaliana), two Cu chaperones, Antioxidant Protein1 (ATX1) and ATX1-Like Copper Chaperone (CCH), share high sequence homology. Previously, their Cu-binding capabilities were demonstrated and interacting molecules were identified. To understand the physiological functions of these two chaperones, we characterized the phenotype of atx1 and cch mutants and the cchatx1 double mutant in Arabidopsis. The shoot and root growth of atx1 and cchatx1 but not cch was specifically hypersensitive to excess Cu but not excess iron, zinc, or cadmium. The activities of antioxidant enzymes in atx1 and cchatx1 were markedly regulated in response to excess Cu, which confirms the phenotype of Cu hypersensitivity. Interestingly, atx1 and cchatx1 were sensitive to Cu deficiency. Overexpression of ATX1 not only enhanced Cu tolerance and accumulation in excess Cu conditions but also tolerance to Cu deficiency. In addition, the Cu-binding motif MXCXXC of ATX1 was required for these physiological functions. ATX1 was previously proposed to be involved in Cu homeostasis by its Cu-binding activity and interaction with the Cu transporter Heavy metal-transporting P-type ATPase5. In this study, we demonstrate that ATX1 plays an essential role in Cu homeostasis in conferring tolerance to excess Cu and Cu deficiency. The possible mechanism is discussed.
authors.affiliation: Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan.
authors.forename: Lung-Jiun
authors.initials: LJ
authors.lastname: Shin
authors.forename: Jing-Chi
authors.initials: JC
authors.lastname: Lo
authors.forename: Kuo-Chen
authors.initials: KC
authors.lastname: Yeh
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000975:Antioxidants / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D003300:Copper / Q000172:deficiency / Q000378:metabolism* / Q000633:toxicity; D000079922:Copper Transport Proteins; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D015227:Lipid Peroxidation / Q000187:drug effects; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D030821:Plants, Genetically Modified; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics; D013329:Structure-Activity Relationship
chemical_list: C575858:ATX1 copper chaperone, Arabidopsis; D000975:Antioxidants; D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; D000079922:Copper Transport Proteins; D018832:Molecular Chaperones; D002734:Chlorophyll; D003300:Copper