Late-stage maturation of the Rieske Fe/S protein: Mzm1 stabilizes Rip1 but does not facilitate its translocation by the AAA ATPase Bcs1

Tie Zhong Cui, Pamela M. Smith, Jennifer L. Fox, Oleh Khalimonchuk, Dennis R. Winge

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33 Scopus citations


The final step in the assembly of the ubiquinol-cytochrome c reductase or bc1 complex involves the insertion of the Rieske Fe/S cluster protein, Rip1. Maturation of Rip1 occurs within the mitochondrial matrix prior to its translocation across the inner membrane (IM) in a process mediated by the Bcs1 ATPase and subsequent insertion into the bc1 complex. Here we show that the matrix protein Mzm1 functions as a Rip1 chaperone, stabilizing Rip1 prior to the translocation step. In the absence of Mzm1, Rip1 is prone to either proteolytic degradation or temperature-induced aggregation. A series of Rip1 truncations were engineered to probe motifs necessary for Mzm1 interaction and Bcs1-mediated translocation of Rip1. The Mzm1 interaction with Rip1 persists in Rip1 variants lacking its transmembrane domain or containing only its C-terminal globular Fe/S domain. Replacement of the globular domain of Rip1 with that of the heterologous folded protein Grx3 abrogated Mzm1 interaction; however, appending the C-terminal 30 residues of Rip1 to the Rip1-Grx3 chimera restored Mzm1 interaction. The Rip1-Grx3 chimera and a Rip1 truncation containing only the N-terminal 92 residues each induced stabilization of the bc1:cytochrome oxidase supercomplex in a Bcs1-dependent manner. However, the Rip1 variants were not stably associated with the supercomplex. The induced supercomplex stabilization by the Rip1 N terminus was independent of Mzm1.

Original languageEnglish (US)
Pages (from-to)4400-4409
Number of pages10
JournalMolecular and cellular biology
Issue number21
StatePublished - Nov 1 2012


ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology

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