title: Impaired folding of the mitochondrial small TIM chaperones induces clearance by the i-AAA protease.
abstract: The intermembrane space of mitochondria contains a dedicated chaperone network-the small translocase of the inner membrane (TIM) family-for the sorting of hydrophobic precursors. All small TIMs are defined by the presence of a twin CX(3)C motif and the monomeric proteins are stabilized by two intramolecular disulfide bonds formed between the cysteines of these motifs. The conserved cysteine residues within small TIM members have also been shown to participate in early biogenesis events, with the most N-terminal cysteine residue important for import and retention within the intermembrane space via the receptor and disulfide oxidase, Mia40. In this study, we have analyzed the in vivo consequences of improper folding of small TIM chaperones by generating site-specific cysteine mutants and assessed the fate of the incompletely oxidized proteins within mitochondria. We show that no individual cysteine residue is required for the function of Tim9 or Tim10 in yeast and that defective assembly of the small TIMs induces their proteolytic clearance from mitochondria. We delineate a clearance mechanism for the mutant proteins and their unassembled wild-type partner protein by the mitochondrial ATP-dependent protease, Yme1 (yeast mitochondrial escape 1).
authors.affiliation: Department of Biochemistry, La Trobe Institute for Molecular Science and ARC Centre of Excellence for Coherent X-ray Science, La Trobe University, Melbourne 3086, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Baker
authors.forename: Ved P
authors.initials: VP
authors.lastname: Mooga
authors.forename: Bernard
authors.initials: B
authors.lastname: Guiard
authors.forename: Thomas
authors.initials: T
authors.lastname: Langer
authors.forename: Michael T
authors.initials: MT
authors.lastname: Ryan
authors.forename: Diana
authors.initials: D
authors.lastname: Stojanovski
mesh_terms: D049069:ATP-Dependent Proteases / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D017510:Protein Folding; D059748:Proteolysis; D012441:Saccharomyces cerevisiae / Q000378:metabolism / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D050505:Mutant Proteins; D029701:Saccharomyces cerevisiae Proteins; C107250:TIM10 protein, S cerevisiae; C116366:Tim9 protein, S cerevisiae; D049069:ATP-Dependent Proteases; C082702:YME1 protein, S cerevisiae