title: Cytosolic factor- and TOM-independent import of C-tail-anchored mitochondrial outer membrane proteins.
abstract: C-tail-anchored (C-TA) proteins are anchored to specific organelle membranes by a single transmembrane segment (TMS) at the C-terminus, extruding the N-terminal functional domains into the cytoplasm in which the TMS and following basic segment function as the membrane-targeting signals. Here, we analyzed the import route of mitochondrial outer membrane (MOM) C-TA proteins, Bak, Bcl-XL, and Omp25, using digitonin-permeabilized HeLa cells, which provide specific and efficient import under competitive conditions. These experiments revealed that (i) C-TA proteins were imported to the MOM through a common pathway independent of the components of the preprotein translocase of the outer membrane, (ii) the C-TA protein-targeting signal functioned autonomously in the absence of cytoplasmic factors that specifically recognize the targeting signals and deliver the preproteins to the MOM, (iii) the function of a cytoplasmic chaperone was required if the cytoplasmic domains of the C-TA proteins assumed an import-incompetent conformation, and intriguingly, (iv) the MOM-targeting signal of Bak, in the context of the Bak molecule, required activation by the interaction of its cytoplasmic domain with VDAC2 before MOM targeting.
authors.affiliation: Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka, Japan.
authors.forename: Kiyoko
authors.initials: K
authors.lastname: Setoguchi
authors.forename: Hidenori
authors.initials: H
authors.lastname: Otera
authors.forename: Katsuyoshi
authors.initials: K
authors.lastname: Mihara
mesh_terms: D003600:Cytosol / Q000378:metabolism*; D019286:Endopeptidase K / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D050995:Voltage-Dependent Anion Channel 1 / Q000378:metabolism; D050996:Voltage-Dependent Anion Channel 2 / Q000378:metabolism; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism
chemical_list: D033681:Mitochondrial Membrane Transport Proteins; D018832:Molecular Chaperones; D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; C494762:VDAC1 protein, human; C494765:VDAC2 protein, human; D050996:Voltage-Dependent Anion Channel 2; D050998:bcl-2 Homologous Antagonist-Killer Protein; D050995:Voltage-Dependent Anion Channel 1; D019286:Endopeptidase K