The transmembrane segment of Tom20 is recognized by Mim1 for docking to the mitochondrial TOM complex.
Mitochondria cannot be made de novo. Mitochondrial biogenesis requires that up to 1000 proteins are imported into mitochondria, and the protein import pathway relies on hetero-oligomeric translocase complexes in both the inner and outer mitochondrial membranes. The translocase in the outer membrane, the TOM complex, is composed of a core complex formed from the beta-barrel channel Tom40 and additional subunits each with single, alpha-helical transmembrane segments. How alpha-helical transmembrane segments might be assembled onto a transmembrane beta-barrel in the context of a membrane environment is a question of fundamental importance. The master receptor subunit of the TOM complex, Tom20, recognizes the targeting sequence on incoming mitochondrial precursor proteins, binds these protein ligands, and then transfers them to the core complex for translocation across the outer membrane. Here we show that the transmembrane segment of Tom20 contains critical residues essential for docking the Tom20 receptor into its correct environment within the TOM complex. This crucial docking reaction is catalyzed by the unique assembly factor Mim1/Tom13. Mutations in the transmembrane segment that destabilize Tom20, or deletion of Mim1, prevent Tom20 from functioning as a receptor for protein import into mitochondria.
Hulett
Joanne M
JM
Department of Biochemistry and Molecular Biology, University of Melbourne, Melbourne 3010, Australia.
Lueder
Franziska
F
Chan
Nickie C
NC
Perry
Andrew J
AJ
Wolynec
Peter
P
Likić
Vladimir A
VA
Gooley
Paul R
PR
Lithgow
Trevor
T
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D017124:Conserved Sequence; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D051336:Mitochondrial Membranes / Q000737:chemistry / Q000378:metabolism; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D002352:Carrier Proteins; C492709:MIM1 protein, S cerevisiae; D008565:Membrane Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D029701:Saccharomyces cerevisiae Proteins; C489350:TOM20 protein, S cerevisiae