JXB Advance Access originally published online on August 30, 2005
Journal of Experimental Botany 2005 56(420):2695-2703; doi:10.1093/jxb/eri262
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RESEARCH PAPER |
Metal binding by citrus dehydrin with histidine-rich domains
Faculty of Agriculture, Shizuoka University, 836 Ohya, Shizuoka 422-8529, Japan
* To whom correspondence should be addressed. Fax: +81 54 238 4881. E-mail: masahara{at}agr.shizuoka.ac.jp
Dehydrins are hydrophilic proteins that are responsive to osmotic stress, such as drought, cold, and salinity in plants. Although they have been hypothesized to stabilize macromolecules in stressed cells, their functions are not fully understood. Citrus dehydrin, which accumulates mainly in response to cold stress, enhances cold tolerance in transgenic tobacco by reducing lipid peroxidation. It has been demonstrated that citrus dehydrin scavenges hydroxyl radicals. In this study, the metal binding of citrus dehydrin is reported and the specific domain responsible is identified. The metal binding property of citrus dehydrin was tested using immobilized metal ion affinity chromatography (IMAC). Fe3+, Co2+, Ni2+, Cu2+, and Zn2+ bound to citrus dehydrin, but Mg2+, Ca2+, and Mn2+ did not. Among the bound metals, the highest affinity was detected for Cu2+-dehydrin binding, which showed a dissociation constant of 1.6 µM. Citrus dehydrin was able to bind up to 16 Cu2+ ions. IMAC indicated that His residues contributed to Cu2+-dehydrin binding. The amino acid sequence of CuCOR15 was divided into five domains, of which domain 1 bound Cu2+ most strongly. One portion of domain 1, HKGEHHSGDHH, was the core sequence for the binding. These results suggest that citrus dehydrin binds metals using a specific sequence containing His. Since citrus dehydrin is a radical-scavenging protein, it may reduce metal toxicity in plant cells under water-stressed conditions.
Key words: Citrus unshiu Marcov., cold stress, dehydrin, LEA proteins, metal binding, osmotic stress
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