The role of Cox20 in Cox2 maturation and cytochrome C oxidase assembly

Proper assembly of Cytochrome c Oxidase (CcO) is vital to mitochondrial respiration. The metallation and incorporation of CcO subunit 2 (Cox2) are important assembly steps that remain poorly understood. The Cox2 assembly factor Cox20 may provide a unique window on CcO assembly. Cox20 is known to bind Cox2 before the latter is incorporated into the larger CcO assembly in S. cerevisiae. Conservation of Cox20 in higher organisms and the lethality of its deletion in Drosophila melanogaster may suggest Cox20 plays a conserved role in CcO assembly. In an attempt to understand the nature of the hypothesized conserved role of Cox20, conserved residues within Cox20 were mutated and the resulting mutants studied. Mutation of a conserved cysteine pair impacted mitochondrial respiration, but did not block CcO assembly. The mutant Cox20 C87A forms a mixed disulfide species. Identifying the partner molecule may shed light on the role of Cox20. The present study finds Cox20, a 23 kD protein, in high molecular weight complexes that are unlikely to be homo-oligomeric. Identifying any other proteins in these complexes may shed light on the role Cox20 plays in CcO assembly. To this end, Cox20 was purified and analyzed by mass spectrometry (MS) to identify any accompanying proteins. Small quantities of the known CcO assembly factors Mss2, Coa1, and Mss51 were identified.