Modulation of Redox Switches of Copper Chaperone Cox17 by Zn(II) Ions Determined by New ESI MS-Based Approach

Abstract

Cox17, a copper chaperone for cytochrome-c oxidase, contains six conserved Cys residues and exists in three oxidative states, linked with two thiol-based redox switches. The first switch leads to formation of two disulfides and occurs upon transport of Cox17 into mitochondrial intermembrane space (IMS). Cox17_2S-S is retained in the IMS and is also a functional form of the protein, which can be further oxidized to Cox17_3S-S. According to the midpoint redox potential values, Cox17 can be partially oxidized in the cytosol, which might hinder its transport into IMS. We hypothesize that Zn(II) ions might protect cytosolic Cox17 from oxidation. In order to get quantitative information about the modulatory effect of Zn(II) ions on redox switches in Cox17, we have used ESI MS for determination of the midpoint potentials for redox couples of Cox17: Cox17_3S-S ↔ Cox17_2S-S (E_m1) and Cox17_2S-S ↔ Cox17_0S-S (E_m2) in the presence of Zn(II). 10 μM Zn(II) ions shift the E_m2 by 21 mV and E_m1 by 15 mV to more positive values. Apparent dissociation constants for Zn(II) complexes of Cox17_0S-S and Cox17_2S-S, are 0.067 and 0.29 nM, respectively. The high affinity shows that metallation of Cox17_0S-S by Zn(II) might be significant in cellular conditions, which might protect Cox17 from oxidation and enable its transport into IMS.

Antioxid. Redox Signal.

11, 985–995.