Mitochondrial thiol oxidase Erv1: Both shuttle cysteine residues are required for its function with distinct roles

Erv1 (essential for respiration and viability 1), is an essential component of the MIA (mitochondrial import and assembly) pathway, playing an important role in the oxidative folding of mitochondrial intermembrane space proteins. In the MIA pathway, Mia40, a thiol oxidoreductase with a CPC motif at its active site, oxidizes newly imported substrate proteins. Erv1 a FAD-dependent thiol oxidase, in turn reoxidizes Mia40 via its N-terminal Cys³⁰-Cys ³³ shuttle disulfide. However, it is unclear how the two shuttle cysteine residues of Erv1 relay electrons from the Mia40 CPC motif to the Erv1 active-site Cys¹³⁰-Cys¹³³ disulfide. In the present study, using yeast genetic approaches we showed that both shuttle cysteine residues of Erv1 are required for cell growth. In organelle and in vitro studies confirmed that both shuttle cysteine residues were indeed required for import of MIA pathway substrates and Erv1 enzyme function to oxidize Mia40. Furthermore, our results revealed that the two shuttle cysteine residues of Erv1 are functionally distinct. Although Cys³³ is essential for forming the intermediate disulfide Cys³³-Cys^130' and transferring electrons to the redox active-site directly, Cys³⁰ plays two important roles: (i) dominantly interacts and receives electrons from the Mia40CPC motif; and (ii) resolves the Erv1 Cys³³-Cys¹³⁰ intermediate disulfide. Taken together, we conclude that both shuttle cysteine residues are required for Erv1 function, and play complementary, but distinct, roles to ensure rapid turnover of active Erv1.