A.thaliana HHC1 is a copper chaperone

LLASES, MARÍA EUGENIA; A. J. VILA; GIANNINI ESTEFANÍA; LISA, MARIÁ-NATALIA

Encuentro; 11th International Copper Research Meeting, Sorrento, Italy, 2018.; 2018

Copper isan essential cofactor of cytochrome c oxidase (COX), the terminal oxidase ofthe respiratory chain in most organisms. COX I and COX II are the twocopper-containing subunits harboring the CuB and CuAsites, respectively, conserved in heme-copper oxidases. Assembly of the oxidaseis a complex process involving the synthesis and folding of the individualsubunits and the incorporation of the metal cofactors.1,2 Scoproteins belong to a family of proteins related to thioredoxins that containtwo redox-active cysteine residues, and a histidine involved in copper binding.2These proteins have been shown to be essential in the assembly of the CuAsite, from subunit COX II. However, their role and the number of essential Scoorthologs differs among organisms. Indeed, the can act as Thiol-Oxidoreductasesand/or copper chaperones in CuA assembly. Previously, we have proposed distinct mechanisms involving Sco proteinsfor the assembly of CuA sites in Bacterial and Human oxidases.3,4 Arabidopsis thaliana HHC1, is a protein fromthe Sco family that is essential for COX activity and plant viability.5,6 Here wereport the biochemical, structural and functional characterization of thisprotein (renamed as AtSco1). AtSco1 is able to bind either Cu(I) or Cu(II)with high affinities (Kd~10-18), in contrast to most Scoproteins. The crystal structure of the soluble fragment of Cu(I)-AtSco1 reveals a Cys2Hiscoordination environment. The Cu(II) variant, instead, shows a tetrahedralenvironment, as revealed by several spectroscopic techniques. To test the biochemical function of AtSco1, we constructed a chimericprotein within the scaffold of the stable T.thermophilus COX II including the metal binding loops of the Arabidopsis COX II. Cu(II)-AtSco1 is able to elicit reduction ofthe oxidized oxidase, and transfer copper ions with a slow kinetics. Instead, Cu(I)-AtSco1 is an efficient copper metallochaperonefor COX II, but is devoid of any redox activity either in the metallated or apoform. Overall, these data reveal that AtSco1is a Cu(I) metallochaperone, while its role as oxidoreductase is still unclear.This picture provides a different scenario regarding Sco functions compared tothat reported for the bacterial periplasmic proteins and the humanmitochondrial ones.