Modulation of the Respiratory Supercomplexes in Yeast: ENHANCED FORMATION OF CYTOCHROME OXIDASE INCREASES THE STABILITY AND ABUNDANCE OF RESPIRATORY SUPERCOMPLEXES*

Yeast cells deficient in the Rieske iron-sulfur subunit (Rip1) of ubiquinol-cytochrome c reductase (bc₁) accumulate a late core assembly intermediate, which weakly associates with cytochrome oxidase (CcO) in a respiratory supercomplex. Expression of the N-terminal half of Rip1, which lacks the C-terminal FeS-containing globular domain (designated N-Rip1), results in a marked stabilization of trimeric and tetrameric bc₁-CcO supercomplexes. Another bc₁ mutant (qcr9Δ) stalled at the same assembly intermediate is likewise converted to stable supercomplex species by the expression of N-Rip1, but not by expression of intact Rip1. The N-Rip1-induced stabilization of bc₁-CcO supercomplexes is independent of the Bcs1 translocase, which mediates Rip1 translocation during bc₁ biogenesis. N-Rip1 induces the stabilization of bc₁-CcO supercomplexes through an enhanced formation of CcO. The association of N-Rip1 with the late core bc₁ assembly intermediate appears to confer stabilization of a CcO assembly intermediate. This induced stabilization of CcO is dependent on the Rcf1 supercomplex stabilization factor and only partially dependent on the presence of cardiolipin. N-Rip1 exerts a related induction of CcO stabilization in WT yeast, resulting in enhanced respiration. Additionally, the impact of CcO stabilization on supercomplexes was observed by means other than expression of N-Rip1 (via overexpression of CcO subunits Cox4 and Cox5a), demonstrating that this is a general phenomenon. This study presents the first evidence showing that supercomplexes can be stabilized by the stimulated formation of CcO.