Our data demonstrate that CMC1 acts in the intermembrane space to stabilize the COX1\COX14\COA3 complex prior to the incorporation of subunits COX4 and COX5a. CIV assembly factors relevant to COX1 metallation (COX10, COX11, and SURF1) or late stability (MITRAC7). Furthermore, whereas human COX14 and COA3 have been proposed to affect COX1 mRNA translation, our data indicate that CMC1 regulates turnover of newly synthesized COX1 prior to and during COX1 maturation, without affecting the rate of COX1 synthesis. oxidase, mitochondrial respiratory chain oxidase that reduces oxygen to water. CIV also contributes to the creation of the proton gradient across the inner membrane that drives ATP synthesis through oxidative phosphorylation (OXPHOS). CIV deficiencies in humans severely affect cellular aerobic energy production and therefore are a common cause of encephalo\ and cardiomyopathies 1. Human CIV contains 14 subunits. The three catalytic subunits (COX1, COX2, and COX3) are encoded in the mitochondrial genome. The remaining subunits (COX4, COX5a, COX5b, COX7a, COX6c, COX7c, COX6b, COX6a, COX7b, COX8, NDUFA4), some of which have tissue\specific isoforms, are nucleus\encoded, synthesized in the cytoplasm, and imported into mitochondria. The CIV redox centers are located in subunits COX1 and COX2. COX1 harbors a heme center and a binuclear heme have shown that the two major targets for regulation are COX1 WW298 synthesis and incorporation of metal prosthetic groups. In COX1mRNA translation is regulated by heme B availability 7, and heme A biosynthesis is regulated by both an early CIV assembly intermediate 8 and COX1\dependent oligomerization of the heme O synthase COX10 9. Furthermore, Cox1 synthesis is Rabbit Polyclonal to NPHP4 WW298 coordinated with its assembly into CIV by the existence of a negative feedback loop 10, 11. In Mss51 is a mRNA\specific translation activator that also interacts with Cox1 protein and Cox1\specific chaperones Cox14 and Coa3 in a stable complex 11, 12, 13. Only when Cox1 proceeds in the assembly pathway, Mss51 is released and becomes available for new rounds of Cox1 synthesis 11. This system serves in part to prevent the accumulation of WW298 partially matured or unassembled Cox1, which can be deleterious 14. In humans, COX1 synthesis is specifically activated by the late\onset Leigh’s syndrome protein TACO1 15, which does not interact with COX1. However, although a functional human homolog of yeast Mss51 has not been identified, mitochondrial cardiomyopathy proteins COA3 (also called MITRAC12, COX25, or CCDC56) and COX14 (or C12orf62) are both COX1 chaperones that interact with newly synthesized WW298 COX1 and drive it through the entire CIV assembly process 16, 17, 18, 19. Human WW298 CIV assembly intermediates containing newly synthesized COX1 and imported respiratory chain subunits have been termed MITRAC complexes 19. Intriguingly, it has been proposed that MITRAC complexes, and specifically the COX1\COX14\COA3 complex, could regulate COX1 synthesis in humans as it occurs in center formation in bacteria 23 but never in mitochondria, is also part of these MITRAC complexes 19. More recent work has identified a new MITRAC component, termed MITRAC7, which affects the biogenesis pathway by stabilizing newly synthesized COX1 in assembly intermediates that contain COX14 and COA3 and also subunits COX4 and COX6c. These observations have suggested the living of a quality control checkpoint during CIV assembly that regulates COX1 turnover 20. The list of CIV assembly factors includes several users of the twin CX9C motif family of proteins, which contain two structural disulfide bonds and are located in the intermembrane space 24, 25, 26. The tasks of these proteins in the CIV assembly process remain in most instances enigmatic. Only COX17, a CIV\specific copper chaperone, has a identified function in copper delivery to metallochaperones COX11 and SCO1/2 for further delivery to COX1 or COX2, respectively 27, 28, 29, 30, 31, 32, 33. Additional twin CX9C proteins known to be critical for CIV assembly/stability/function in and/or human being cells include the mitochondrial cardiomyopathy proteins PET191 and COA6 34, 35, 36 as well as Cmc1, Cmc2, Cox19, and Cox23 37, 38, 39,.