Assembly of Tom6 and Tom7 into the TOM Core Complex ofNeurospora crassa

Dembowski, Markus; Künkele, Klaus Peter; Nargang, Frank E.; Neupert, Walter; Rapaport, Doron

doi:10.1074/jbc.m009653200

Cited by 62 publications

(53 citation statements)

References 33 publications

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“…Fungal Tom7 is part of an ϳ400-kDa general import pore complex where it is tightly associated with the channel-forming protein Tom40 (15,18,20,21,39). We asked whether human Tom7 could be imported into mammalian mitochondria and assembled into the TOM complex in the outer membrane.…”

Section: Resultsmentioning

confidence: 99%

“…The human cDNA contains a 165-bp ORF encoding a protein of 55 amino acids with a predicted molecular mass of 6.2 kDa. An amino acid alignment of the human ORF with known Tom7 orthologs from the yeast S. cerevisiae, (18), N. crassa (39), and potato (Solanum tuberosum (40)) along with putative Tom7 proteins from Caenorhabditis elegans (GenBank TM accession number P34660) and mouse (Mus musculus, GenBank TM accession number W74865) revealed that they all contain the conserved motif aGaX-PXXXXXG where a is an aromatic residue and X is any residue (Fig. 1A).…”

Section: Resultsmentioning

confidence: 99%

“…The presence of such an intermediate has not been reported previously. Fungal Tom7, on the other hand, assembles into preexisting 400-kDa TOM complexes (15,19,20,39). The assembly of human Tom7 via this intermediate resembles that observed for the import of yeast Tom6.…”

Section: Figmentioning

confidence: 95%

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Insertion and Assembly of Human Tom7 into the Preprotein Translocase Complex of the Outer Mitochondrial Membrane

Johnston¹,

Hoogenraad²,

Dougan³

et al. 2002

Journal of Biological Chemistry

128

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Tom7 is a component of the translocase of the outer mitochondrial membrane (TOM) and assembles into a general import pore complex that translocates preproteins into mitochondria. We have identified the human Tom7 homolog and characterized its import and assembly into the mammalian TOM complex. Tom7 is imported into mitochondria in a nucleotide-independent manner and is anchored to the outer membrane with its C terminus facing the intermembrane space. Unlike studies in fungi, we found that human Tom7 assembles into an ϳ120-kDa import intermediate in HeLa cell mitochondria. To detect subunits within this complex, we employed a novel supershift analysis whereby mitochondria containing newly imported Tom7 were incubated with antibodies specific for individual TOM components prior to separation by blue native electrophoresis. We found that the 120-kDa complex contains Tom40 and lacks receptor components. This intermediate can be chased to the stable ϳ380-kDa mammalian TOM complex that additionally contains Tom22. Overexpression of Tom22 in HeLa cells results in the rapid assembly of Tom7 into the 380-kDa complex indicating that Tom22 is rate-limiting for TOM complex formation. These results indicate that the levels of Tom22 within mitochondria dictate the assembly of TOM complexes and hence may regulate its biogenesis.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Insertion and Assembly of Human Tom7 into the Preprotein Translocase Complex of the Outer Mitochondrial Membrane

Johnston¹,

Hoogenraad²,

Dougan³

et al. 2002

Journal of Biological Chemistry

128

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“…The core complex contains the central receptor Tom22 and the channel Tom40 as well as Tom5, Tom6, and Tom7. The three small Tom proteins are involved in protein import and stability of the TOM complex (41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53), although their molecular function is only understood in part. In particular, the function of Tom7, which is well conserved in evolution, is unclear as various findings with pleiotropic and in part contradictory results have been reported.…”

mentioning

confidence: 99%

Mitochondrial Protein Sorting

Meisinger

Wiedemann

Rissler

et al. 2006

Journal of Biological Chemistry

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The mitochondrial outer membrane contains two distinct machineries for protein import and protein sorting that function in a sequential manner: the general translocase of the outer membrane (TOM complex) and the sorting and assembly machinery (SAM complex), which is dedicated to ␤-barrel proteins. The SAM core complex consists of three subunits, Sam35, Sam37, and Sam50, that can associate with a fourth subunit, the morphology component Mdm10, to form the SAM holo complex. Whereas the SAM core complex is required for the biogenesis of all ␤-barrel proteins, Mdm10 and the SAM holo complex play a selective role in ␤-barrel biogenesis by promoting assembly of Tom40 but not of porin. We report that Tom7, a conserved subunit of the TOM complex, functions in an antagonistic manner to Mdm10 in biogenesis of Tom40 and porin. We show that Tom7 promotes segregation of Mdm10 from the SAM holo complex into a low molecular mass form. Upon deletion of Tom7, the fraction of Mdm10 in the SAM holo complex is significantly increased, explaining the opposing functions of Tom7 and Mdm10 in ␤-barrel sorting. Thus the role of Tom7 is not limited to the TOM complex. Tom7 functions in mitochondrial protein biogenesis by a new mechanism, segregation of a sorting component, leading to a differentiation of ␤-barrel assembly.Mitochondria import the vast majority of their ϳ1,000 different proteins from the cytosol (1-3). Upon initial recognition and translocation by the general translocase of the outer mitochondrial membrane (TOM 5 complex), different classes of precursor proteins are distributed to the four mitochondrial subcompartments, outer membrane, intermembrane space, inner membrane, and matrix (4 -11). Preproteins carrying cleavable amino-terminal targeting signals (presequences) are transferred from the TOM complex to the presequence translocase of the inner membrane (TIM23 complex) and then sorted to matrix and inner membrane. Many mitochondrial proteins, however, are synthesized without cleavable presequences, including all outer membrane proteins and the majority of intermembrane space and inner membrane proteins. These proteins use distinct import and sorting machineries. Thus, in addition to the presequence pathway, three sorting pathways for non-cleavable mitochondrial precursor proteins have been identified, each of them starting at the TOM complex. Many hydrophobic inner membrane proteins, including the abundant metabolite carriers, are imported via small Tim proteins of the intermembrane space and the twin pore translocase of the inner membrane (TIM22 complex) (8, 12). Small proteins of the intermembrane space use a special import and assembly machinery that includes Mia40 and the sulfhydryl oxidase Erv1 (13-17). Outer membrane proteins are also initially transported via the TOM complex; however, the TOM complex is not able to integrate ␤-barrel proteins into the membrane. Therefore, the outer membrane contains a separate sorting and assembly machinery (SAM complex) that directs membrane integration and assembly of ␤-barrel...

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“…Tom5 was initially only identi ed in Saccharomyces cerevisiae, but recently has also been detected in Neurospora crassa (Neupert et al, unpublished). Tom6 and Tom7 seem to be involved in the regulation of the assembly and disassembly of receptor proteins with the GIP, a process that is probably mediated by Tom22 (41,48,(54)(55)(56)(57)(58). Recently it was shown in cross-linking experiments that Neurospora crassa Tom6 and Tom7 are in vicinity of preproteins, which are in transit across the outer membrane (58).…”

Section: Translocation Across the Outer Membranementioning

confidence: 99%

Protein Import Into Mitochondria

Paschen¹,

Neupert²

2001

IUBMB Life

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SummaryMost mitochondrial proteins are encoded by the nuclear genome and thus have to be imported into mitochondria from the cytosol. Protein translocation across and into the mitochondrial membranes is a multistep process facilitated by the coordinated action of at least four specialized translocation systems in the outer and inner membranes of mitochondria. The outer membrane contains one general translocase, the TOM complex, whereas three distinct translocases are located in the inner membrane, which facilitates translocation of different classes of preproteins. The TIM23 complex mediates import of matrix-targeted preproteins with Nterminal presequences, whereas hydrophobi c preproteins with internal targeting signals are inserted into the inner membrane via the TIM22 complex. The OXA translocase mediates the insertion of preproteins from the matrix space into the inner membrane. This review focuses on the structural organization and function of the import machinery of the model organisms of Saccharomyces cerevisiae and Neurospora crassa. In addition, the molecular basis of a new human mitochondrial disorder is discussed, the MohrTranebjaerg syndrome. This is the rst known disease, which is caused by an impaired mitochondrial protein import machinery leading to progressive neurodegeneration.

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Assembly of Tom6 and Tom7 into the TOM Core Complex ofNeurospora crassa

Cited by 62 publications

References 33 publications

Insertion and Assembly of Human Tom7 into the Preprotein Translocase Complex of the Outer Mitochondrial Membrane

Insertion and Assembly of Human Tom7 into the Preprotein Translocase Complex of the Outer Mitochondrial Membrane

Mitochondrial Protein Sorting

Protein Import Into Mitochondria

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