Mitochondrial intermembrane space import and assembly protein 40 (CHCHD4) is a chaperone and catalyses the formation of disulfide bonds in proteins within the mitochondrial intermembrane space (IMS) such as COX17 [], COX19 [], MICU1 []and GFER []. A precursor of one of these proteins in a reduced state is imported into the mitochondrion where it associates with CHCHD4 forming a transient intermolecular disulfide bridge. This leads to oxidation of the precursor, formation of an intramolecular disulfide bond and the folding in the IMS [].This entry also includes the uncharacterized protein F42H10.2 from Caenorhabditis elegans.
A conserved motif was identified in the LOC118487 protein was called the CHCH motif. Alignment of this protein with related members showed the presence of three subgroups of proteins, which are called the S (Small), N (N-terminal extended) and C (C-terminal extended) subgroups. All three sub-groups of proteins have in common that they contain a predicted conserved [coiled coil 1]-[helix 1]-[coiled coil 2]-[helix 2]domain (CHCH domain). Within each helix of the CHCH domain, there are two cysteines present in a C-X9-C motif. The N-group contains an additional double helix domain, and each helix contains the C-X9-C motif. This family contains a number of characterised proteins: Cox19 protein - a nuclear gene of Saccharomyces cerevisiae, codes for an 11kDa protein (Cox19p) required for expression of cytochrome oxidase. Because cox19 mutants are able to synthesise the mitochondrial and nuclear gene products of cytochrome oxidase, Cox19p probably functions post-translationally during assembly of the enzyme. Cox19p is present in the cytoplasm and mitochondria, where it exists as a soluble intermembrane protein. This dual location is similar to what was previously reported for Cox17p, a low molecular weight copper protein thought to be required for maturation of the CuA centre of subunit 2 of cytochrome oxidase. Cox19p have four conserved potential metal ligands, these are three cysteines and one histidine. Mrp10 - belongs to the class of yeast mitochondrial ribosomal proteins that are essential for translation []. Eukaryotic NADH-ubiquinone oxidoreductase 19kDa (NDUFA8) subunit []. The CHCH domain was previously called DUF657 [].
