Coa1 links the Mss51 post-translational function to Cox1 cofactor insertion in cytochrome c oxidase assembly

Abstract

The assembly of cytochrome c oxidase (CcO) in yeast mitochondria is shown to be dependent on a new assembly factor designated Coa1 that associates with the mitochondrial inner membrane. Translation of the mitochondrial-encoded subunits of CcO occurs normally in coa1Delta cells, but these subunits fail to accumulate. The respiratory defect in coa1Delta cells is suppressed by high-copy MSS51, MDJ1 and COX10. Mss51 functions in Cox1 translation and elongation, whereas Cox10 participates in the biosynthesis of heme a, a key cofactor of CcO. Respiration in coa1Delta and shy1Delta cells is enhanced when Mss51 and Cox10 are coexpressed. Shy1 has been implicated in formation of the heme a3-Cu(B) site in Cox1. The interaction between Coa1 and Cox1, and the physical and genetic interactions between Coa1 and Mss51, Shy1 and Cox14 suggest that Coa1 coordinates the transition of newly synthesized Cox1 from the Mss51:Cox14 complex to the heme a cofactor insertion involving Shy1. coa1Delta cells also display a mitochondrial copper defect suggesting that Coa1 may have a direct link to copper metallation of CcO.

Mss51 and Ssc1 Facilitate Translational Regulation of Cytochrome c Oxidase Biogenesis

“…2A). Similarly, in ⌬cox14 cells in which Cox1 is normally synthesized but is unstable, Mss51 is detected almost exclusively in the 120-kDa complex as reported (40). The same result was obtained for ⌬oxa1 cells (Fig.…”

“…The reported native MW of Mss51 in wild-type mitochondria varies depending on the extraction conditions (2,40). To standardize these conditions, we tested several KCl, MgCl 2 , and digitonin concentrations.…”

“…According to this model, the release of Mss51 from the ternary complex and its availability for Cox1 synthesis probably occur when Cox1 acquires its prosthetic groups or interacts with other COX subunits, a step possibly catalyzed by Shy1, a protein involved in maturation and/or assembly of Cox1 (2,10,34). Coa1 could also participate in Cox1 maturation and stabilize the ternary Cox1/Mss51/Cox14 complex until it interacts with Shy1 (34,40). Further studies are required to understand how Mss51 is recycled from its posttranslational function to become available for COX1 mRNA translation and to fully clarify how this regulatory mechanism operates.…”

Inaccurately Assembled CytochromecOxidase Can Lead to Oxidative Stress-Induced Growth Arrest

“…6A, B). Diminished levels of Cox1 synthesis are characteristic for strains with defects in the assembly of cytochrome c oxidase (5,21,37,44,45). The levels of Cox1 were not increased in the presence of DTT, indicating that DTT did not suppress the assembly defect in these strains (Fig.…”

“…In particular, assembly intermediates of Cox1 containing heme but no copper killed hydrogen peroxide-treated cytochrome c oxidase mutants on glucose medium. This cytotoxic potential might explain why mitochondrial Cox1 synthesis is under tight feedback control, which prevents the accumulation of assembly intermediates (5,21,37,44,45). At this stage it is not entirely clear where the ROS are produced.…”