Cytochrome c oxidase (COX) or mitochondrial respiratory chain complex IV catalyses the transfer of electrons from intermembrane space cytochrome c to molecular oxygen in the matrix and therefore contributes to the proton gradient involved in mitochondrial ATP synthesis. Complex IV dysfunction is a significant cause of human mitochondrial disease. Biogenesis of complex IV requires assembly factors for subunit maturation, co-factor attachment and stabilization of intermediate assemblies. Copper, a redox active metal, is a vital trace element required by all living organisms, where it acts as an essential cofactor of COX which requires three copper ions for the construction of dinuclear CuA and mononuclear CuB sites, both of which are critical for assembly and activity of the complex. Mutations in several genes encoding assembly factors required for copper delivery to COX result in diminished COX activity and severe pathologic conditions in affected infants.
Our study focuses on two mitochondrial Complex IV assembly factors, Coa6 and Coa7, that are located in the intermembrane space of mitochondria and contain intramolecular disulfide bonds. Coa6 binds Cu(I) with KD ~10-17 M and acts in the Cu-delivery pathway to COX. The W59C pathogenic mutation in Coa6 does not affect copper binding or import of the protein into mitochondria but affects the maturation and stability of the protein. The exact role of Coa7 is still not completely understood, however, its potential role in assembly of the complex IV was reported in vitro in cell culture studies. This presentation will describe the crystal structures of the Coa7, wild-type and the W59C mutant Coa6 proteins and implications for their role in COX assembly and function.