FIG. 3.

The IMS, a redox compartment with different functions. Many unfolded proteins traverse the IMS to reach the inner membrane or to exit mitochondria. The graphic shows the disulfide bridge relay given by the two complementary intermediaries Mia40 and Erv1 in the IMS. The two components compose a cycle by which an unfolded protein with thiol groups forms a disulfide bridge with oxidized Mia40 (Mia40ox) that allows the protein to be refolded with intermolecular disulfide formation and Mia40 reduction. Mia40red returns to its oxidized state by reduction of Erv1, subsequently recovered by given electrons to Cyt c, and ultimately to cytochrome oxidase. MIA40, mitochondrial intermembrane space assembly machinery; ERV1, endogenous retroviral sequence; Cyt c, cytochrome c; COX, cytochrome oxidase; IMM, inner mitochondrial membrane; IMS, intermembrane space; OMM, outer mitochondrial membrane.