RESUMEN
Copper (Cu) chaperones constitute a family of small Cu+-binding proteins required for Cu homeostasis in eukaryotes. The ATX1 family of Cu chaperones specifically delivers Cu to heavy metal P-type ATPases. The plant Arabidopsis thaliana expresses the ATX1-like Cu chaperone CCH, which exhibits a plant-specific carboxy-terminal domain (CTD) with unique structural properties. We show that CCH homologues from other higher plants contain CTDs with structural properties similar to Arabidopsis CCH. Furthermore, we identify a new ATX1-like Cu chaperone in Arabidopsis, AtATX1, which functionally complements yeast atx1Delta and sod1Delta associated phenotypes, and localizes to the cytosol of Arabidopsis cells. Interestingly, AtATX1, but not full-length CCH, interacts in vivo with the Arabidopsis RAN1 Cu-transporting P-type ATPase by yeast two-hybrid. We propose that higher plants express two types of ATX1-like Cu chaperones: the ATX1-type with a predominant function in Cu delivery to P-type ATPases, and the CCH-type with additional CTD-mediated plant-specific functions.
Asunto(s)
Proteínas de Arabidopsis/fisiología , Arabidopsis/química , Cobre/metabolismo , Chaperonas Moleculares/fisiología , Factores de Transcripción/fisiología , Adenosina Trifosfatasas/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , Cobre/química , Genoma de Planta/fisiología , N-Metiltransferasa de Histona-Lisina , Chaperonas Moleculares/química , Chaperonas Moleculares/genética , Estructura Terciaria de Proteína , Factores de Transcripción/química , Factores de Transcripción/genéticaRESUMEN
Copper (Cu) is a micronutrient that has roles in photosynthesis, respiration, antioxidant activity, cell wall metabolism and hormone perception. Excess Cu is toxic and therefore its delivery has to be tightly regulated. Recent progress in the study of Cu homeostasis has revealed not only components of the Cu delivery machinery but also regulatory systems that control Cu-protein expression and coordinate the activity of Cu-delivery systems. The response of photosynthetic organisms to Cu deficiency indicates the existence of cross-talk between metal cofactor delivery pathways. Next to its well-established roles in plant metabolism, a novel function for Cu, first discovered in plants, is in the biogenesis of molybdenum cofactor. Defects in Cu delivery factors also suggest important roles for Cu in cell expansion.
Asunto(s)
Coenzimas/metabolismo , Cobre/metabolismo , Células Vegetales , Plantas/metabolismo , Regulación Enzimológica de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Membranas Intracelulares/metabolismoRESUMEN
In plant chloroplasts two superoxide dismutase (SOD) activities occur, FeSOD and Cu/ZnSOD, with reciprocal regulation in response to copper availability. This system presents a unique model to study the regulation of metal-cofactor delivery to an organelle. The Arabidopsis thaliana gene AtCCS encodes a functional homolog to yeast Ccs1p/Lys7p, a copper chaperone for SOD. The AtCCS protein was localized to chloroplasts where it may supply copper to the stromal Cu/ZnSOD. AtCCS mRNA expression levels are upregulated in response to Cu-feeding and senescence. We propose that AtCCS expression is regulated to allow the most optimal use of Cu for photosynthesis.