title: Tom20 recognizes mitochondrial presequences through dynamic equilibrium among multiple bound states.
abstract: Most mitochondrial proteins are synthesized in the cytosol and imported into mitochondria. The N-terminal presequences of mitochondrial-precursor proteins contain a diverse consensus motif (phi chi chi phi phi, phi is hydrophobic and chi is any amino acid), which is recognized by the Tom20 protein on the mitochondrial surface. To reveal the structural basis of the broad selectivity of Tom20, the Tom20-presequence complex was crystallized. Tethering a presequence peptide to Tom20 through a disulfide bond was essential for crystallization. Unexpectedly, the two crystals with different linker designs provided unique relative orientations of the presequence with respect to Tom20, and neither configuration could fully account for the hydrophobic preference at the three hydrophobic positions of the consensus motif. We propose the existence of a dynamic equilibrium in solution among multiple states including the two bound states. In accordance, NMR 15N relaxation analyses suggested motion on a sub-millisecond timescale at the Tom20-presequence interface. We suggest that the dynamic, multiple-mode interaction is the molecular mechanism facilitating the broadly selective specificity of the Tom20 receptor toward diverse mitochondrial presequences.
authors.affiliation: Division of Structural Biology, Medical Institute of Bioregulation, Kyushu University, Maidashi, Higashi-ku, Fukuoka, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Saitoh
authors.forename: Mayumi
authors.initials: M
authors.lastname: Igura
authors.forename: Takayuki
authors.initials: T
authors.lastname: Obita
authors.forename: Toyoyuki
authors.initials: T
authors.lastname: Ose
authors.forename: Rieko
authors.initials: R
authors.lastname: Kojima
authors.forename: Katsumi
authors.initials: K
authors.lastname: Maenaka
authors.forename: Toshiya
authors.initials: T
authors.lastname: Endo
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kohda
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000737:chemistry / Q000378:metabolism*; D003460:Crystallization; D003461:Crystallography; D009682:Magnetic Resonance Spectroscopy; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism*
chemical_list: D026901:Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D019151:Peptide Library; D010455:Peptides; D011956:Receptors, Cell Surface; C489998:Tomm20 protein, rat; D000444:Aldehyde Dehydrogenase