title: Late-stage maturation of the Rieske Fe/S protein: Mzm1 stabilizes Rip1 but does not facilitate its translocation by the AAA ATPase Bcs1.
abstract: The final step in the assembly of the ubiquinol-cytochrome c reductase or bc(1) 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 bc(1) 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 bc(1):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.
authors.affiliation: University of Utah Health Sciences Center, Department of Medicine, Salt Lake City, Utah, USA.
authors.forename: Tie-Zhong
authors.initials: TZ
authors.lastname: Cui
authors.forename: Pamela M
authors.initials: PM
authors.lastname: Smith
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Fox
authors.forename: Oleh
authors.initials: O
authors.lastname: Khalimonchuk
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Winge
mesh_terms: D000074183:ATPases Associated with Diverse Cellular Activities; D014450:Electron Transport Complex III / Q000096:biosynthesis / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D028861:Nuclear Pore Complex Proteins / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism; D017510:Protein Folding; D025941:Protein Interaction Mapping; D060066:Protein Interaction Maps; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*
chemical_list: C472685:BCS1 protein, S cerevisiae; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D018832:Molecular Chaperones; C109212:NUP42 protein, S cerevisiae; D028861:Nuclear Pore Complex Proteins; C037989:Rieske iron-sulfur protein; D029701:Saccharomyces cerevisiae Proteins; C568504:mitochondrial zinc maintenance protein 1, S cerevisiae; C545181:Grx3 protein, S cerevisiae; D010088:Oxidoreductases; D000074183:ATPases Associated with Diverse Cellular Activities; D014450:Electron Transport Complex III