title: Recognition of mitochondrial targeting sequences by the import receptors Tom20 and Tom22.
abstract: The Tom20 and Tom22 receptor subunits of the TOM (translocase of the outer mitochondrial membrane) complex recognize N-terminal presequences of proteins that are to be imported into the mitochondrion. In plants, Tom20 is C-terminally anchored in the mitochondrial membrane, whereas Tom20 is N-terminally anchored in animals and fungi. Furthermore, the cytosolic domain of Tom22 in plants is smaller than its animal/fungal counterpart and contains fewer acidic residues. Here, NMR spectroscopy was used to explore presequence interactions with the cytosolic regions of receptors from the plant Arabidopsis thaliana and the fungus Saccharomyces cerevisiae (i.e., AtTom20, AtTom22, and ScTom22). It was found that AtTom20 possesses a discontinuous bidentate hydrophobic binding site for presequences. The presequences on plant mitochondrial proteins comprise two or more hydrophobic binding regions to match this bidentate site. NMR data suggested that while these presequences bind to ScTom22, they do not bind to AtTom22. AtTom22, however, binds to AtTom20 at the same binding site as presequences, suggesting that this domain competes with the presequences of imported proteins, thereby enabling their progression along the import pathway.
authors.affiliation: Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Kieran A
authors.initials: KA
authors.lastname: Rimmer
authors.forename: Jung Hock
authors.initials: JH
authors.lastname: Foo
authors.forename: Alicia
authors.initials: A
authors.lastname: Ng
authors.forename: Emma J
authors.initials: EJ
authors.lastname: Petrie
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Shilling
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Perry
authors.forename: Haydyn D T
authors.initials: HD
authors.lastname: Mertens
authors.forename: Trevor
authors.initials: T
authors.lastname: Lithgow
authors.forename: Terrence D
authors.initials: TD
authors.lastname: Mulhern
authors.forename: Paul R
authors.initials: PR
authors.lastname: Gooley
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry*; D001665:Binding Sites; D026901:Membrane Transport Proteins / Q000737:chemistry*; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011956:Receptors, Cell Surface / Q000737:chemistry*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry*
chemical_list: D029681:Arabidopsis Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D011956:Receptors, Cell Surface; D029701:Saccharomyces cerevisiae Proteins; C489350:TOM20 protein, S cerevisiae; C489970:TOM22-I protein, Arabidopsis; C555604:Tom20 protein, Arabidopsis