A detailed analysis of cytochrome C oxidase assembly in yeast mitochondria

Cytochrome c Oxidase (CcO) is the terminal enzyme of the mitochondrial respiratory chain. This complex is comprised of subunits encoded by the nuclear and mitochondrial genomes, and requires heme a and copper cofactors for enzyme activity. The assembly pathway of the CcO complex is a coordinated process requiring numerous assembly proteins important for transcription, translation, membrane insertion/processing, stabilization and cofactor insertion. Genetic disruption of this pathway in humans results in CcO respiratory disorders that target high-energy demanding tissues such as brain, skeletal muscle and kidneys. Much of the characterization of CcO assembly has been determined from assessing the assembled state of CcO from affected patient tissues, as well as corresponding studies in the yeast model system Saccharomyces cerevisiae. The work presented in this dissertation focuses on the mechanism of assembly for copper and heme cofactor centers in yeast CcO, specifically the core subunit Coxl. The copper ions required in CcO are supplied from a matrix pool where copper is bound to a small, anionic ligand. In ongoing studies to identify proteins involved in the recruitment and distribution of mitochondrial copper, Coal was found as a novel CcO assembly factor. Yeast cells lacking Coal showed respiratory deficiency and low mitochondrial copper, a similar phenotype to the known Shyl assembly factor. Extragenic suppressors of the coal A respiratory defect were determined as MSS51, COXIO and C0A2. Suppression by MSS51 and COX 10 linked Coal function to posttranslational stabilization of Coxl and cofactor insertion, as Cox 10 is essential for generating the Coxl-specific heme a cofactor. Coa2 was also identified as a CcO assembly factor, and shown to be important for Coxl stabilization in conjunction with Shyl. Studying the interrelationship between Coa2 and CoxlO indicated a role for Coa2 in the hemylation of Coxl. Mutations in SURF1, the human ortholog of SHY1, cause a CcO deficiency resulting in Leigh syndrome. Characterization of corresponding mutations made in Shyl identified a new CcO assembly factor YLR218c, which we present for future studies. Understanding the details of the CcO assembly process will give insight into the mechanism of human disease and could suggest potential therapies.