Mitochondrial intermembrane space import and assembly protein 40 (Chchd4)

Functions as chaperone and catalyzes the formation of disulfide bonds in substrate proteins, such as COX17, COX19 and MICU1. Required for the import and folding of small cysteine- containing proteins (small Tim) from the mitochondrial intermembrane space (IMS).

Precursor proteins to be imported into the IMS are translocated in their reduced form into the mitochondria. The oxidized form of CHCHD4/MIA40 forms a transient intermolecular disulfide bridge with the reduced precursor protein, resulting in oxidation of the precursor protein that now contains an intramolecular disulfide bond and can undergo folding in the IMS.