Folding Studies of Cox17 Reveal an Important Interplay of Cysteine Oxidation and Copper Binding

SummaryCox17 is a key mitochondrial copper chaperone involved in the assembly of cytochrome c oxidase (COX). The NMR solution structure of the oxidized apoCox17 isoform consists of a coiled-coil conformation stabilized by two disulfide bonds involving Cys26/Cys57 and Cys36/Cys47. This appears to be a conserved tertiary fold of a class of proteins, localized within the mitochondrial intermembrane space, that contain a twin Cys-x9-Cys sequence motif. An isomerization of one disulfide bond from Cys26/Cys57 to Cys24/Cys57 is required prior to Cu(I) binding to form the Cu1Cox17 complex. Upon further oxidation of the apo-protein, a form with three disulfide bonds is obtained. The reduction of all disulfide bonds provides a molten globule form that can convert to an additional conformer capable of binding up to four Cu(I) ions in a polycopper cluster. This form of the protein is oligomeric. These properties are framed within a complete model of mitochondrial import and COX assembly