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Vol. 18, Issue 5, 1897-1908, May 2007

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Oxa1 Directly Interacts with Atp9 and Mediates Its Assembly into the Mitochondrial F₁F_o-ATP Synthase Complex

Department of Biological Sciences, Marquette University, Milwaukee, WI 53233

Submitted October 18, 2006; Revised January 29, 2007; Accepted February 26, 2007
Monitoring Editor: Janet Shaw

The yeast Oxa1 protein is involved in the biogenesis of the mitochondrial oxidative phosphorylation (OXPHOS) machinery. The involvement of Oxa1 in the assembly of the cytochrome oxidase (COX) complex, where it facilitates the cotranslational membrane insertion of mitochondrially encoded COX subunits, is well documented. In this study we have addressed the role of Oxa1, and its sequence-related protein Cox18/Oxa2, in the biogenesis of the F₁F_o-ATP synthase complex. We demonstrate that Oxa1, but not Cox18/Oxa2, directly supports the assembly of the membrane embedded F_o-sector of the ATP synthase. Oxa1 was found to physically interact with newly synthesized mitochondrially encoded Atp9 protein in a posttranslational manner and in a manner that is not dependent on the C-terminal, matrix-localized region of Oxa1. The stable manner of the Atp9-Oxa1 interaction is in contrast to the cotranslational and transient interaction previously observed for the mitochondrially encoded COX subunits with Oxa1. In the absence of Oxa1, Atp9 was observed to assemble into an oligomeric complex containing F₁-subunits, but its further assembly with subunit 6 (Atp6) of the F_o-sector was perturbed. We propose that by directly interacting with newly synthesized Atp9 in a posttranslational manner, Oxa1 is required to maintain the assembly competence of the Atp9-F₁-subcomplex for its association with Atp6.

Address correspondence to: Rosemary A. Stuart (rosemary.stuart{at}marquette.edu)

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