Cmc1p Is a Conserved Mitochondrial Twin CX₉C Protein Involved in Cytochrome c Oxidase Biogenesis

Abstract

Copper is an essential cofactor of two mitochondrial enzymes: cytochrome c oxidase (COX) and Cu-Zn superoxide dismutase (Sod1p). Copper incorporation into these enzymes is facilitated by metallochaperone proteins which probably use copper from a mitochondrial matrix-localized pool. Here we describe a novel conserved mitochondrial metallochaperone-like protein, Cmc1p, whose function affects both COX and Sod1p. In Saccharomyces cerevisiae, Cmc1p localizes to the mitochondrial inner membrane facing the intermembrane space. Cmc1p is essential for full expression of COX and respiration, contains a twin CX 9 C domain conserved in other COX assembly copper chaperones, and has the ability to bind copper(I). Additionally, mutant cmc1 cells display increased mitochondrial Sod1p activity, while CMC1 overexpression results in decreased Sod1p activity. Our results suggest that Cmc1p could play a direct or indirect role in copper trafficking and distribution to COX and Sod1p.

Import, Maturation, and Function of SOD1 and Its Copper Chaperone CCS in the Mitochondrial Intermembrane Space

“…How mutant G93A SOD1 causes COX deficiency is not clear, but it could be speculated that SOD1 and COX, both cupro-enzymes, compete for the same pool of copper in mitochondria. Supporting this hypothesis, as mentioned earlier, ablation of the IMS copper-transferring protein, Cmc1p, increases levels of active SOD1 but decreases COX activity (27). A recent study in NSC34 cells expressing inducible G93A mutant SOD1 suggested that COX deficiency is due to increased nitric oxide levels, rather than copper depletion, because copper supplementation did not rescue COX activity, but nitric oxide scavengers did (2).…”

“…Recently, a yeast protein embedded in the IM, Cmc1p, was shown to be critical for the distribution of copper to COX and SOD1 (27). It was shown that ablation of Cmc1p expression results in decreased COX assembly and activity…”

“…3. Proposed pathway of copper distribution to the mitochondrial cupro-enzymes, COX and SOD1 (27). This scheme was kindly provided by Drs.…”

“…The increase in SOD1 enzymatic activity was not due to increased protein content, and therefore presumably linked to enhanced copper delivery to the enzyme. It was proposed that Cmc1p delivers copper to COX through its copper chaperones (cox17 and cox19, and Sco proteins), and that it may draw from the same copper pool in the IMS that CCS uses (27) (Fig. 3).…”

Copper Import into the Mitochondrial Matrix in Saccharomyces cerevisiae Is Mediated by Pic2, a Mitochondrial Carrier Family Protein

“…The soluble intermembrane space (IMS) protein Cox17 delivers copper to both Sco1 and Cox11, which are integral inner membrane (IM) proteins that donate copper to the assembling holoenzyme (8,9). Additionally, the IMS protein Cmc1 has been implicated in the control of copper flow within the IMS, potentially by directing copper to the Cox17-mediated CcO assembly pathway (10).…”