title: Novel mitochondrial intermembrane space proteins as substrates of the MIA import pathway.
abstract: Mitochondria consist of four compartments, the outer membrane, intermembrane space (IMS), inner membrane and the matrix. Most mitochondrial proteins are synthesized as precursors in the cytosol and have to be imported into these compartments. While the protein import machineries of the outer membrane, inner membrane and matrix have been investigated in detail, a specific mitochondrial machinery for import and assembly of IMS proteins, termed MIA, was identified only recently. To date, only a very small number of substrate proteins of the MIA pathway have been identified. The substrates contain characteristic cysteine motifs, either a twin Cx(3)C or a twin Cx(9)C motif. The largest MIA substrates known possess a molecular mass of 11 kDa, implying that this new import pathway has a very small size limit. Here, we have compiled a list of Saccharomyces cerevisiae proteins with a twin Cx(9)C motif and identified three IMS proteins that were previously localized to incorrect cellular compartments by tagging approaches. Mdm35, Mic14 (YDR031w) and Mic17 (YMR002w) require the two essential subunits, Mia40 and Erv1, of the MIA machinery for their localization in the mitochondrial IMS. With a molecular mass of 14 kDa and 17 kDa, respectively, Mic14 and Mic17 are larger than the known MIA substrates. Remarkably, the precursor of Erv1 itself is imported via the MIA pathway. As Erv1 has a molecular mass of 22 kDa and a twin Cx(2)C motif, this study demonstrates that the MIA pathway can transport substrates that are twice as large as the substrates known to date and is not limited to proteins with twin Cx(3)C or Cx(9)C motifs. However, tagging of MIA substrates can interfere with their subcellular localization, indicating that the proper localization of mitochondrial IMS proteins requires the characterization of the authentic untagged proteins.
authors.affiliation: Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany.
authors.forename: Kipros
authors.initials: K
authors.lastname: Gabriel
authors.forename: Dusanka
authors.initials: D
authors.lastname: Milenkovic
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Chacinska
authors.forename: Judith
authors.initials: J
authors.lastname: Müller
authors.forename: Bernard
authors.initials: B
authors.lastname: Guiard
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Pfanner
authors.forename: Chris
authors.initials: C
authors.lastname: Meisinger
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000378:metabolism*; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D050862:Oxidoreductases Acting on Sulfur Group Donors; D011498:Protein Precursors / Q000378:metabolism; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: C495320:MIA40 protein, S cerevisiae; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D011498:Protein Precursors; D029701:Saccharomyces cerevisiae Proteins; D050862:Oxidoreductases Acting on Sulfur Group Donors; C073790:ERV1 protein, S cerevisiae