Targeting of the Master Receptor MOM19 to Mitochondria

Schneider, Hans‐Jürgen; Söllner, Thomas H.; Dietmeier, Klaus; Eckerskorn, Christoph; Lottspeich, F.; Trülzsch, Barbara; Neupert, Walter; Pfanner, Nikolaus

doi:10.1126/science.1661031

Cited by 116 publications

(73 citation statements)

References 28 publications

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“…This result shows that pre-existing Tom20 is not absolutely required for the correct import of newly synthesized Tom20 precursors. In agreement with this, import in vitro of newly synthesized Tom20 was found not to be dependent on the presence of cytosolic domains of import receptors (22). Expression of a Tom20 variant that lacked the signal-anchor domain (residues 1-36) did not restore growth on a non-fermentable carbon source ( Fig.…”

Section: Resultssupporting

confidence: 75%

Signal-Anchor Domains of Proteins of the Outer Membrane of Mitochondria

Waizenegger

Stan

Neupert

et al. 2003

Journal of Biological Chemistry

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We have studied the topogenesis of a class of mitochondrial outer membrane proteins that expose a hydrophilic domain to the cytosol and are anchored to the membrane by a single transmembrane domain in the N-terminal region. To determine the role of these latter sequences in the targeting and insertion of such proteins we took two approaches. First, a functional complementation assay was used to define the structural elements that together with the anchor domain make up the topogenic signal. Moderate hydrophobicity of the transmembrane domain was found to be the most important requirement. Variants with a scrambled sequence of the membrane-spanning segment were only partially functional suggesting that specificity in the amino acid sequence is also of considerable importance. A net positive charge at both flanking regions of the transmembrane domain contributes to the efficiency of targeting and membrane integration but is not an essential structural feature of this signal. Second, chimeras of Tom20, Tom70, and OM45 were generated that contained the cytosolic domain of Tom20 or Tom70 and the anchor domain of one of the other members of the class. These hybrid proteins were able to rescue the growth of cells lacking Tom20 or Tom70. Thus, anchor domains of outer membrane proteins are functionally interchangeable. They play only a minor role in the specific function of these proteins, but have a decisive role in topogenic signaling.The targeting of most mitochondrial preproteins is mediated by cleavable N-terminal extensions of about 20 -50 amino acid residues (the presequences or matrix-targeting signals), which are necessary and sufficient to direct them into the mitochondria (1, 2). Yet, all preproteins of the mitochondrial outer membrane are devoid of a typical N-terminal presequence. The targeting information is rather contained in the protein sequence itself.A special class of mitochondrial outer membrane proteins includes those containing a single transmembrane segment at their N-terminal. The three known members of this class are Tom20, Tom70, and OM45 ( Fig. 1) (3). These proteins are present in the outer membrane in an orientation, where the bulk of the polypeptide is exposed to the cytosol and only a small N-terminal segment crosses the outer membrane. They are called "signal-anchored" proteins since their TMD 1 together with its flanking regions serve both as an intracellular sorting signal and as an anchor to the membrane. Tom20 and Tom70 are examples of this class of proteins. They function as receptor proteins that mediate the import of preproteins. Tom20 is involved in the translocation of most protein precursors, in particular those with N-terminal targeting signals (4, 5), whereas Tom70 forms a binding site for a more restricted set of preproteins, most notably the mitochondrial carrier family (6 -8). OM45, another member of this class, is a very abundant protein in the yeast mitochondrial outer membrane whose function, however, is unknown (9).The contribution of the signal-anchor domain to the fun...

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Section: Resultssupporting

confidence: 75%

Signal-Anchor Domains of Proteins of the Outer Membrane of Mitochondria

Waizenegger

Stan

Neupert

et al. 2003

Journal of Biological Chemistry

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“…The yeast homologue ISP42 (Import Site Protein of 42 kDa) is essential for cell viability [12]. Antibodies against N. crassa MOM38 can inhibit the assembly of N. crassa MOM19 into the outer membrane of isolated yeast mitochondria reflecting the high evolutionary conservation of the mitochondrial import system [13]. In a genetic approach ISP6 was characterised as a multi-copy suppressor for the mutant ISP42 allele [14].…”

Section: The Receptor Complex Of the Outer Membranementioning

confidence: 99%

Mitochondrial protein import: Mechanisms, components and energetics

Schwarz

Neupert

1994

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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The transport of nuclear-encoded proteins from the cytosol into mitochondria is mediated by targeting (signal) sequences present on precursor forms. Most precursors of the mitochondrial matrix possess amino-terminal signals which characteristically contain hydroxylated and basic amino acids and lack acidic residues. With a minority of precursor proteins, internal sequence motifs can direct proteins to the mitochondria (Planner, N., Hoeben, P., Tropschug, M. and Neupert, W. (1987) J. Biol. Chem. 262, 14851-14854). The presence of a mitochondrial targeting sequence alone, however, is not sufficient for specific targeting to the organeUe and further to the various subcompartments. There is the need for components which recognise the targeting sequences and others which keep the precursor protein in a translocation-competent form. Beyond the recognition step, components are required which mediate transiocation across the mitochondrial membranes. Mitochondria possess two translocation machineries, one in the outer membrane and one in the inner membrane. The matrix space harbors a number of factors which participate in the import of proteins, in their unfolding and folding. Energy is required at several steps of these processes.

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“…Unlike the matrix-targeted preproteins with cleavable presequences, the signals that target the outer membrane proteins are contained within the mature protein sequence. The import receptors of the preprotein translocase of the mitochondrial outer membrane (TOM 1 complex (3), Tom70 (4,5), and Tom20 (6,7)) are anchored to the membrane through the N-terminal ␣-helical transmembrane domain (TMD) in the Nin-Cout orientation. Tom22, which functions as the preprotein receptor and organizer of the TOM complex, is anchored to the outer membrane in the Nout-Cin orientation through a TMD in the middle portion of the molecule (8 -11).…”

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Targeting and Assembly of Rat Mitochondrial Translocase of Outer Membrane 22 (TOM22) into the TOM Complex

Nakamura

Suzuki

Sakaguchi

et al. 2004

Journal of Biological Chemistry

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Tom22 is a preprotein receptor and organizer of the mitochondrial outer membrane translocase complex (TOM complex). Rat Tom22 (rTOM22) is a 142-residue protein, embedded in the outer membrane through the internal transmembrane domain (TMD) with 82 N-terminal residues in the cytosol and 41 C-terminal residues in the intermembrane space. We analyzed the signals that target rTOM22 to the mitochondrial outer membrane and assembly into the TOM complex in cultured mammalian cells. Deletions or mutations were systematically introduced into the molecule, and the intracellular localization of the mutant constructs in HeLa cells was examined by confocal microscopy and cell fractionation. Their assembly into the TOM complex was also examined using blue native gel electrophoresis. These experiments revealed three separate structural elements: a cytoplasmic 10-residue segment with an acidic ␣-helical structure located 30 residues upstream of the TMD (the import sequence), TMD with an appropriate hydrophobicity, and a 20-residue C-terminal segment located 22 residues downstream of the TMD (C-tail signal). The import sequence and TMD were both essential for targeting and integration into the TOM complex, whereas the C-tail signal affected the import efficiency. The import sequence combined with foreign TMD functioned as a mitochondrial targeting and anchor signal but failed to integrate the construct into the TOM complex. Thus, the mitochondrial-targeting and TOM integration signal could be discriminated. A yeast two-hybrid assay revealed that the import sequence interacted with two intramolecular elements, the TMD and C-tail signal, and that it also interacted with the import receptor Tom20.

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Targeting of the Master Receptor MOM19 to Mitochondria

Abstract: (Neuron, in press) as previously described (6). Cultures used for recording had been maintained in vitro for 12 to Ther. 7, 6 (1984)]. Nystatin patch electrodes [R. Horn and A. Marty, J. Gen. Physiol. 92, 145 (1988)

Cited by 116 publications

References 28 publications

Signal-Anchor Domains of Proteins of the Outer Membrane of Mitochondria

Signal-Anchor Domains of Proteins of the Outer Membrane of Mitochondria

Mitochondrial protein import: Mechanisms, components and energetics

Targeting and Assembly of Rat Mitochondrial Translocase of Outer Membrane 22 (TOM22) into the TOM Complex

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