InterPro domain: IPR005616

Members of this family include NrfF, CcmH, CycL, Ccl2. CcmH proteins possess an RCXXC motif exposed to the periplasm. This motif is believed to be active in the reduction of the cysteines of the CXXCH motif on apocytochromes c [ 1 ]. In Arabidopsis, AtCCMH (At1g15220) is a mitochondrial protein that plays a central role in mitochondrial cytochrome c maturation [ 2 ]. It forms a complex with CcmF and performs the assembly of heme with c-type apocytochromes in plant mitochondria [ 2 , 3 ]. NrfF is not required for the biogenesis of c-type cytochromes [ 4 ].

1. AtCCMH, an essential component of the c-type cytochrome maturation pathway in Arabidopsis mitochondria, interacts with apocytochrome c. Proc. Natl. Acad. Sci. U.S.A. 102, 16113-8
2. The three mitochondrial encoded CcmF proteins form a complex that interacts with CCMH and c-type apocytochromes in Arabidopsis. J. Biol. Chem. 283, 25200-8
3. Biochemical properties and catalytic domain structure of the CcmH protein from Escherichia coli. Biochim. Biophys. Acta 1824, 1394-400
4. The role of the genes nrf EFG and ccmFH in cytochrome c biosynthesis in Escherichia coli. Mol. Gen. Genet. 252, 332-41