scholarly journals How does the TOM complex mediate insertion of precursor proteins into the mitochondrial outer membrane?

2005 ◽  
Vol 171 (3) ◽  
pp. 419-423 ◽  
Author(s):  
Doron Rapaport
Keyword(s):  
Membrane Proteins ◽  
Outer Membrane ◽  
Mitochondrial Membrane ◽  
Mitochondrial Outer Membrane ◽  
Outer Face ◽  
Outer Mitochondrial Membrane ◽  
Lipid Core ◽  
Tom Complex ◽  
Precursor Proteins

A multisubunit translocase of the outer mitochondrial membrane (TOM complex) mediates both the import of mitochondrial precursor proteins into the internal compartments of the organelle and the insertion of proteins residing in the mitochondrial outer membrane. The proposed β-barrel structure of Tom40, the pore-forming component of the translocase, raises the question of how the apparent uninterrupted β-barrel topology can be compatible with a role of Tom40 in releasing membrane proteins into the lipid core of the bilayer. In this review, I discuss insertion mechanisms of proteins into the outer membrane and present alternative models based on the opening of a multisubunit β-barrel TOM structure or on the interaction of outer membrane precursors with the outer face of the Tom40 β-barrel structure.

scholarly journals Role of Phosphatidylethanolamine in the Biogenesis of Mitochondrial Outer Membrane Proteins

2013 ◽  
Vol 288 (23) ◽  
pp. 16451-16459 ◽  
Author(s):  
Thomas Becker ◽  
Susanne E. Horvath ◽  
Lena Böttinger ◽  
Natalia Gebert ◽  
Günther Daum ◽  
...  
Keyword(s):  
Membrane Proteins ◽  
Outer Membrane ◽  
Outer Membrane Proteins ◽  
Proper Function ◽  
Mitochondrial Outer Membrane ◽  
Tom Complex ◽  
Precursor Proteins ◽  
Helical Proteins ◽  
The Stability

The mitochondrial outer membrane contains proteinaceous machineries for the import and assembly of proteins, including TOM (translocase of the outer membrane) and SAM (sorting and assembly machinery). It has been shown that the dimeric phospholipid cardiolipin is required for the stability of TOM and SAM complexes and thus for the efficient import and assembly of β-barrel proteins and some α-helical proteins of the outer membrane. Here, we report that mitochondria deficient in phosphatidylethanolamine (PE), the second non-bilayer-forming phospholipid, are impaired in the biogenesis of β-barrel proteins, but not of α-helical outer membrane proteins. The stability of TOM and SAM complexes is not disturbed by the lack of PE. By dissecting the import steps of β-barrel proteins, we show that an early import stage involving translocation through the TOM complex is affected. In PE-depleted mitochondria, the TOM complex binds precursor proteins with reduced efficiency. We conclude that PE is required for the proper function of the TOM complex.

scholarly journals A discrete pathway for the transfer of intermembrane space proteins across the outer membrane of mitochondria

2014 ◽  
Vol 25 (25) ◽  
pp. 3999-4009 ◽  
Author(s):  
Agnieszka Gornicka ◽  
Piotr Bragoszewski ◽  
Piotr Chroscicki ◽  
Lena-Sophie Wenz ◽  
Christian Schulz ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Mitochondrial Membrane ◽  
Alternative Pathway ◽  
Intermembrane Space ◽  
Outer Mitochondrial Membrane ◽  
Membrane Translocation ◽  
Tom Complex ◽  
Precursor Proteins ◽  
Core Components

Mitochondrial proteins are synthesized on cytosolic ribosomes and imported into mitochondria with the help of protein translocases. For the majority of precursor proteins, the role of the translocase of the outer membrane (TOM) and mechanisms of their transport across the outer mitochondrial membrane are well recognized. However, little is known about the mode of membrane translocation for proteins that are targeted to the intermembrane space via the redox-driven mitochondrial intermembrane space import and assembly (MIA) pathway. On the basis of the results obtained from an in organello competition import assay, we hypothesized that MIA-dependent precursor proteins use an alternative pathway to cross the outer mitochondrial membrane. Here we demonstrate that this alternative pathway involves the protein channel formed by Tom40. We sought a translocation intermediate by expressing tagged versions of MIA-dependent proteins in vivo. We identified a transient interaction between our model substrates and Tom40. Of interest, outer membrane translocation did not directly involve other core components of the TOM complex, including Tom22. Thus MIA-dependent proteins take another route across the outer mitochondrial membrane that involves Tom40 in a form that is different from the canonical TOM complex.

Synthesis of intracellular membrane proteins in vitro. Relation between rough endoplasmic reticulum and mitochondrial outer membrane

1979 ◽  
Vol 38 (1) ◽  
pp. 137-153
Author(s):  
G.C. Shore
Keyword(s):  
Membrane Proteins ◽  
Outer Membrane ◽  
Mitochondrial Membrane ◽  
Polyacrylamide Gel Electrophoresis ◽  
Mitochondrial Outer Membrane ◽  
Major Protein ◽  
Outer Mitochondrial Membrane ◽  
Reticulocyte Lysate ◽  
Dependent Protein

Hepatic rough microsomes were incubated in a messenger-dependent protein-synthesizing system from rabbit reticulocytes. Up to 30% of the total product labelled with [35S]methionine, and subsequently recovered with the microsomes, was located in an intrinsic protein fraction associated with these membranes, i.e. was retained by the membrane following extensive sonication in the presence of 1.5 M KCl, 0.1% deoxycholate, and 5 mM ethylenediaminetetra-acetate (EDTA). When products synthesized with the use of membrane-free mRNA from rough microsomes and free polysome were post-incubated with rough microsomes, ribosome-stripped rough microsomes, or outer mitochondrial membrane, low amounts of intrinsic-type polypeptide product were recovered with these membranes. Higher recovery was achieved, however, when ribosome-stripped rough microsomes were added at the beginning of polypeptide synthesis in a reticulocyte lysate supplemented with additional ribosomal-wash factors. Analysis of these products by polyacrylamide gel electrophoresis showed that a number co-migrated with intrinsic proteins located in both rough microsomes and mitochondrial outer membrane. In addition, a prominent in vitro product co-migrated with a major protein which is located in outer mitochondrial membrane fractions, but is barely detectable in rough microsomal fractions. The present experiments were unable to detect a unique set of intrinsic polypeptides which were synthesized and assembled in vitro under the direction of mRNA from free polysomes, and not from rough microsomes. The results suggest that synthesis of at least some intrinsic membrane proteins which are destined for the outer mitochondrial membrane occurs on rough ER in rat liver.

scholarly journals Functions of the Small Proteins in the TOM Complex of Neurospora crasssa

2005 ◽  
Vol 16 (9) ◽  
pp. 4172-4182 ◽  
Author(s):  
E. Laura Sherman ◽  
Nancy E. Go ◽  
Frank E. Nargang
Keyword(s):  
Mitochondrial Membrane ◽  
Minor Role ◽  
Complex Stability ◽  
Outer Mitochondrial Membrane ◽  
The Core ◽  
Tom Complex ◽  
Membrane Complex ◽  
Small Proteins ◽  
Precursor Proteins ◽  
A Minor

The TOM (translocase of the outer mitochondrial membrane) complex of the outer mitochondrial membrane is required for the import of proteins into the organelle. The core TOM complex contains five proteins, including three small components Tom7, Tom6, and Tom5. We have created single and double mutants of all combinations of the three small Tom proteins of Neurospora crassa. Analysis of the mutants revealed that Tom6 plays a major role in TOM complex stability, whereas Tom7 has a lesser role. Mutants lacking both Tom6 and Tom7 have an extremely labile TOM complex and are the only class of mutant to exhibit an altered growth phenotype. Although single mutants lacking N. crassa Tom5 have no apparent TOM complex abnormalities, studies of double mutants lacking Tom5 suggest that it also has a minor role in maintaining TOM complex stability. Our inability to isolate triple mutants supports the idea that the three proteins have overlapping functions. Mitochondria lacking either Tom6 or Tom7 are differentially affected in their ability to import different precursor proteins into the organelle, suggesting that they may play roles in the sorting of proteins to different mitochondrial subcompartments. Newly imported Tom40 was readily assembled into the TOM complex in mitochondria lacking any of the small Tom proteins.

scholarly journals Role of the intermembrane-space domain of the preprotein receptor Tom22 in protein import into mitochondria.

1996 ◽  
Vol 16 (8) ◽  
pp. 4035-4042 ◽  
Author(s):  
D A Court ◽  
F E Nargang ◽  
H Steiner ◽  
R S Hodges ◽  
W Neupert ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Protein Import ◽  
Protein Translocation ◽  
Specific Binding ◽  
Mitochondrial Outer Membrane ◽  
Intermembrane Space ◽  
Inner Membrane ◽  
Terminal Domain ◽  
Tom Complex

Tom22 is an essential component of the protein translocation complex (Tom complex) of the mitochondrial outer membrane. The N-terminal domain of Tom22 functions as a preprotein receptor in cooperation with Tom20. The role of the C-terminal domain of Tom22, which is exposed to the intermembrane space (IMS), in its own assembly into the Tom complex and in the import of other preproteins was investigated. The C-terminal domain of Tom22 is not essential for the targeting and assembly of this protein, as constructs lacking part or all of the IMS domain became imported into mitochondria and assembled into the Tom complex. Mutant strains of Neurospora expressing the truncated Tom22 proteins were generated by a novel procedure. These mutants displayed wild-type growth rates, in contrast to cells lacking Tom22, which are not viable. The import of proteins into the outer membrane and the IMS of isolated mutant mitochondria was not affected. Some but not all preproteins destined for the matrix and inner membrane were imported less efficiently. The reduced import was not due to impaired interaction of presequences with their specific binding site on the trans side of the outer membrane. Rather, the IMS domain of Tom22 appears to slightly enhance the efficiency of the transfer of these preproteins to the import machinery of the inner membrane.

scholarly journals The mitochondrial import protein Mim1 promotes biogenesis of multispanning outer membrane proteins

2011 ◽  
Vol 194 (3) ◽  
pp. 387-395 ◽  
Author(s):  
Thomas Becker ◽  
Lena-Sophie Wenz ◽  
Vivien Krüger ◽  
Waltraut Lehmann ◽  
Judith M. Müller ◽  
...  
Keyword(s):  
Membrane Proteins ◽  
Outer Membrane ◽  
Outer Membrane Proteins ◽  
Mitochondrial Outer Membrane ◽  
Limited Information ◽  
Mitochondrial Import ◽  
Transmembrane Segments ◽  
Membrane Complex ◽  
Complex Functions ◽  
Precursor Proteins

The mitochondrial outer membrane contains translocase complexes for the import of precursor proteins. The translocase of the outer membrane complex functions as a general preprotein entry gate, whereas the sorting and assembly machinery complex mediates membrane insertion of β-barrel proteins of the outer membrane. Several α-helical outer membrane proteins are known to carry multiple transmembrane segments; however, only limited information is available on the biogenesis of these proteins. We report that mitochondria lacking the mitochondrial import protein 1 (Mim1) are impaired in the biogenesis of multispanning outer membrane proteins, whereas overexpression of Mim1 stimulates their import. The Mim1 complex cooperates with the receptor Tom70 in binding of precursor proteins and promotes their insertion and assembly into the outer membrane. We conclude that the Mim1 complex plays a central role in the import of α-helical outer membrane proteins with multiple transmembrane segments.

scholarly journals An essential novel component of the noncanonical mitochondrial outer membrane protein import system of trypanosomatids

2012 ◽  
Vol 23 (17) ◽  
pp. 3420-3428 ◽  
Author(s):  
Mascha Pusnik ◽  
Jan Mani ◽  
Oliver Schmidt ◽  
Moritz Niemann ◽  
Silke Oeljeklaus ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Outer Membrane ◽  
Outer Membrane Protein ◽  
Protein Import ◽  
Matrix Proteins ◽  
Mitochondrial Outer Membrane ◽  
Outer Mitochondrial Membrane ◽  
Precursor Proteins ◽  
Substrate Proteins ◽  
Import System

The mitochondrial outer membrane protein Tom40 is the general entry gate for imported proteins in essentially all eukaryotes. Trypanosomatids lack Tom40, however, and use instead a protein termed the archaic translocase of the outer mitochondrial membrane (ATOM). Here we report the discovery of pATOM36, a novel essential component of the trypanosomal outer membrane protein import system that interacts with ATOM. pATOM36 is not related to known Tom proteins from other organisms and mediates the import of matrix proteins. However, there is a group of precursor proteins whose import is independent of pATOM36. Domain-swapping experiments indicate that the N-terminal presequence-containing domain of the substrate proteins at least in part determines the dependence on pATOM36. Secondary structure profiling suggests that pATOM36 is composed largely of α-helices and its assembly into the outer membrane is independent of the sorting and assembly machinery complex. Taken together, these results show that pATOM36 is a novel component associated with the ATOM complex that promotes the import of a subpopulation of proteins into the mitochondrial matrix.

scholarly journals Biogenesis of Porin of the Outer Mitochondrial Membrane Involves an Import Pathway via Receptors and the General Import Pore of the Tom Complex

2001 ◽  
Vol 152 (2) ◽  
pp. 289-300 ◽  
Author(s):  
Thomas Krimmer ◽  
Doron Rapaport ◽  
Michael T. Ryan ◽  
Chris Meisinger ◽  
C. Kenneth Kassenbrock ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Mitochondrial Membrane ◽  
Anion Channel ◽  
Mitochondrial Outer Membrane ◽  
Outer Mitochondrial Membrane ◽  
Voltage Dependent Anion Channel ◽  
Surface Receptors ◽  
Voltage Dependent ◽  
Surface Receptor

Porin, also termed the voltage-dependent anion channel, is the most abundant protein of the mitochondrial outer membrane. The process of import and assembly of the protein is known to be dependent on the surface receptor Tom20, but the requirement for other mitochondrial proteins remains controversial. We have used mitochondria from Neurospora crassa and Saccharomyces cerevisiae to analyze the import pathway of porin. Import of porin into isolated mitochondria in which the outer membrane has been opened is inhibited despite similar levels of Tom20 as in intact mitochondria. A matrix-destined precursor and the porin precursor compete for the same translocation sites in both normal mitochondria and mitochondria whose surface receptors have been removed, suggesting that both precursors utilize the general import pore. Using an assay established to monitor the assembly of in vitro–imported porin into preexisting porin complexes we have shown that besides Tom20, the biogenesis of porin depends on the central receptor Tom22, as well as Tom5 and Tom7 of the general import pore complex (translocase of the outer mitochondrial membrane [TOM] core complex). The characterization of two new mutant alleles of the essential pore protein Tom40 demonstrates that the import of porin also requires a functional Tom40. Moreover, the porin precursor can be cross-linked to Tom20, Tom22, and Tom40 on its import pathway. We conclude that import of porin does not proceed through the action of Tom20 alone, but requires an intact outer membrane and involves at least four more subunits of the TOM machinery, including the general import pore.

scholarly journals Dissecting the interactions of PINK1 with the TOM complex in depolarized mitochondria

2022 ◽  
Author(s):  
Klaudia Maruszczak ◽  
Martin Jung ◽  
Shafqat Rasool ◽  
Jean-Francois Trempe ◽  
Doron Rapaport
Keyword(s):  
Parkinson’S Disease ◽  
Outer Membrane ◽  
Molecular Mechanism ◽  
Mitochondrial Outer Membrane ◽  
Structural Protein ◽  
Mitochondria Dysfunction ◽  
Tom Complex ◽  
The Individual ◽  
Import Receptor

Mitochondria dysfunction is involved in the pathomechanism of many illnesses including Parkinson's disease. PINK1, which is mutated in some cases of familiar Parkinsonism, is a key component in the degradation of damaged mitochondria by mitophagy. The accumulation of PINK1 on the mitochondrial outer membrane (MOM) of compromised organelles is crucial for the induction of mitophagy, but the molecular mechanism of this process is still unresolved. Here, we investigate the association of PINK1 with the TOM complex. We demonstrate that PINK1 heavily relies on the import receptor TOM70 for its association with mitochondria and directly interacts with this receptor. The structural protein TOM7 appears to play only a moderate role in PINK1 association with the TOM complex, probably due to its role in stabilizing this complex. PINK1 requires the TOM40 pore lumen for its stable interaction with the TOM complex and apparently remains there during its further association with the MOM. Overall, this study provides new insights on the role of the individual TOM subunits in the association of PINK1 with the MOM of depolarized mitochondria.

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