title: Protein translocase of the outer mitochondrial membrane: role of import receptors in the structural organization of the TOM complex.
abstract: The mitochondrial outer membrane contains a multi-subunit machinery responsible for the specific recognition and translocation of precursor proteins. This translocase of the outer membrane (TOM) consists of three receptor proteins, Tom20, Tom22 and Tom70, the channel protein Tom40, and several small Tom proteins. Single-particle electron microscopy analysis of the Neurospora TOM complex has led to different views with two or three stain-filled centers resembling channels. Based on biochemical and electron microscopy studies of the TOM complex isolated from yeast mitochondria, we have discovered the molecular reason for the different number of channel-like structures. The TOM complex from wild-type yeast contains up to three stain-filled centers, while from a mutant yeast selectively lacking Tom20, the TOM complex particles contain only two channel-like structures. From mutant mitochondria lacking Tom22, native electrophoresis separates an approximately 80 kDa subcomplex that consists of Tom40 only and is functional for accumulation of a precursor protein. We conclude that while Tom40 forms the import channels, the two receptors Tom22 and Tom20 are required for the organization of Tom40 dimers into larger TOM structures.
authors.affiliation: Department of Structural Biology, Max-Planck-Institut für Biophysik, Frankfurt am Main, Germany.
authors.forename: Kirstin
authors.initials: K
authors.lastname: Model
authors.forename: Thorsten
authors.initials: T
authors.lastname: Prinz
authors.forename: Teresa
authors.initials: T
authors.lastname: Ruiz
authors.forename: Michael
authors.initials: M
authors.lastname: Radermacher
authors.forename: Thomas
authors.initials: T
authors.lastname: Krimmer
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Pfanner
authors.forename: Chris
authors.initials: C
authors.lastname: Meisinger
mesh_terms: D005656:Fungal Proteins / Q000378:metabolism; D017353:Gene Deletion; D007425:Intracellular Membranes / Q000201:enzymology*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008928:Mitochondria / Q000201:enzymology* / Q000235:genetics; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D009491:Neurospora / Q000201:enzymology; D011498:Protein Precursors / Q000378:metabolism; D020836:Protein Structure, Quaternary; D021381:Protein Transport; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D005656:Fungal Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D011498:Protein Precursors; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D029701:Saccharomyces cerevisiae Proteins; C489350:TOM20 protein, S cerevisiae; C090857:TOM22 protein, S cerevisiae; C489039:TOM70 protein, S cerevisiae; C066555:Tom40 protein, S cerevisiae