title: Tom5 functionally links mitochondrial preprotein receptors to the general import pore.
abstract: Most mitochondrial proteins are synthesized as preproteins on cytosolic polysomes and are subsequently imported into the organelle. The mitochondrial outer membrane contains a multisubunit preprotein translocase (Tom) which has receptors on the cytosolic side and a general import pore (GIP) in the membrane. Tom20-Tom22 and Tom70-Tom37 function as import receptors with a preference for preproteins that have amino-terminal presequences or internal targeting information, respectively. Tom40 is an essential constituent of the GIP, whereas Tom6 and Tom7 modulate the assembly and dissociation of the Tom machinery. Here we report the identification of Tom5, a small subunit that has a crucial role importing preproteins destined for all four mitochondrial subcompartments. Tom5 has a single membrane anchor and a cytosolic segment with a negative net charge, and accepts preproteins from the receptors and mediates their insertion into the GIP. We conclude that Tom5 represents a functional link between surface receptors and GIP, and is part of an 'acid chain' that guides the stepwise transport of positively charged mitochondrial targeting sequences.
authors.affiliation: Institut für Biochemie und Molekularbiologie, Universität Freiburg, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Dietmeier
authors.forename: A
authors.initials: A
authors.lastname: Hönlinger
authors.forename: U
authors.initials: U
authors.lastname: Bömer
authors.forename: P J
authors.initials: PJ
authors.lastname: Dekker
authors.forename: C
authors.initials: C
authors.lastname: Eckerskorn
authors.forename: F
authors.initials: F
authors.lastname: Lottspeich
authors.forename: M
authors.initials: M
authors.lastname: Kübrich
authors.forename: N
authors.initials: N
authors.lastname: Pfanner
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008969:Molecular Sequence Data; D018272:Porins / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins
chemical_list: C037688:ADP-ATP carrier receptor; D002352:Carrier Proteins; D005656:Fungal Proteins; D008565:Membrane Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D018272:Porins; D011498:Protein Precursors; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; C106794:TOM5 protein, S cerevisiae