Cox16 protein is physically associated with Cox1p assembly intermediates and with cytochrome oxidase [Membrane Biology]

Mitochondrial cytochrome oxidase (COX) catalyzes the last step in the respiratory pathway. In Saccharomyces cervisiae this inner membrane complex is composed of 11 protein subunits. Expression of COX is assisted by some 2 dozen ancillary proteins that intercede at different stages of the assembly pathway. One such protein, Cox16p, encoded by COX16, was shown to be essential for activity and assembly of COX. The function of Cox16p, however, has not been determined. We present evidence that Cox16p is present in Cox1p assembly intermediates and in COX. This is based on the finding that Cox16p, tagged with a dual poly-histidine and protein C tag, co-immunopurified with Cox1p assembly intermediates. The pull-down assays also indicated the presence of Cox16p in mature COX and in supercomplexes consisting of COX and the bc1 complex. From the Western signal strengths, Cox16p appears to be substoichiometric with Cox1p and Cox4p, which could indicate that Cox16p is only present in a fraction of COX. In conclusion, our results indicate that Cox16p is a constituent of several Cox1p assembly intermediates and of COX.

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