TOM40/YMR203W Summary Help

Standard Name TOM40 1
Systematic Name YMR203W
Alias ISP42 2 , MOM38
Feature Type ORF, Verified
Description Component of the TOM (translocase of outer membrane) complex; responsible for recognition and initial import steps for all mitochondrially directed proteins; constitutes the core element of the protein conducting pore; pre-Tom40p is phosphorylated by PKA, which impairs its import into mitochondria under non-respiratory conditions (3, 4, 5, 6, 7, 8 and see Summary Paragraph)
Name Description Translocase of the Outer Mitochondrial membrane 1
Chromosomal Location
ChrXIII:668492 to 669655 | ORF Map | GBrowse
Gbrowse
Gene Ontology Annotations All TOM40 GO evidence and references
  View Computational GO annotations for TOM40
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
High-throughput
Regulators 5 genes
Resources
Classical genetics
conditional
null
overexpression
repressible
Large-scale survey
null
reduction of function
Resources
93 total interaction(s) for 39 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 7
  • Affinity Capture-RNA: 3
  • Affinity Capture-Western: 48
  • Biochemical Activity: 3
  • Co-fractionation: 9
  • Co-purification: 5
  • PCA: 2
  • Reconstituted Complex: 6

Genetic Interactions
  • Dosage Growth Defect: 2
  • Dosage Rescue: 4
  • Positive Genetic: 2
  • Synthetic Lethality: 2

Resources
Expression Summary
histogram
Resources
Length (a.a.) 387
Molecular Weight (Da) 42,038
Isoelectric Point (pI) 5.27
Localization
Phosphorylation PhosphoGRID | PhosphoPep Database
Structure
Homologs
sequence information
ChrXIII:668492 to 669655 | ORF Map | GBrowse
SGD ORF map
Last Update Coordinates: 2011-02-03 | Sequence: 1996-07-31
Subfeature details
Relative
Coordinates
Chromosomal
Coordinates
Most Recent Updates
Coordinates Sequence
CDS 1..1164 668492..669655 2011-02-03 1996-07-31
Retrieve sequences
Analyze Sequence
S288C only
S288C vs. other species
S288C vs. other strains
Resources
External Links All Associated Seq | Entrez Gene | Entrez RefSeq Protein | MIPS | Search all NCBI (Entrez) | UniProtKB
Primary SGDIDS000004816
SUMMARY PARAGRAPH for TOM40

About mitochondrial import

While the mitochondrial genome encodes a handful of proteins, most of the hundreds of proteins that reside in the mitochondrion are encoded by nuclear genes, translated in the cytoplasm, and imported into mitochondria via a series of complex molecular machines (see 9, 10 for review). Many of the proteins imported into mitochondria are involved in respiration, which is not an essential process: S. cerevisiae is able to carry out either fermentative growth on carbon sources such as glucose, or respiratory growth on nonfermentable carbon sources such as glycerol and ethanol. However, since maintenance of the mitochondrial compartment is essential to life, mutations that completely disrupt mitochondrial import are lethal.

About the TOM complex

The first step of import is mediated by the translocase of the outer mitochondrial membrane (TOM) complex, composed of the subunits Tom70p, Tom40p, Tom22p, Tom20p, Tom7p, Tom6p, and Tom5p (11, 12). Tom70p and Tom20p are both integral membrane proteins with cytosolic domains that act as receptors for incoming proteins. Tom70p interacts with hydrophobic precursor proteins via its tetratricopeptide repeats (13), while Tom20p interacts with precursor proteins that have N-terminal mitochondrial targeting signals (14). Tom70p also interacts with cytosolic Hsp70 family chaperones of the Ssa subfamily in order to receive preproteins from these chaperones (15). Tom40p and the three small (50-70 residues) proteins Tom5p, Tom6p, and Tom7p comprise the membrane pore for protein translocation, often referred to as the general import pore or GIP (12, 16). Tom40p has a beta-barrel structure and forms the membrane pore (17, 18, 19). The three small proteins are individually dispensable for function of the pore, but at least one of the three is absolutely required (20, 21). Tom22p appears to have a structural role in the complex and may also contribute to binding of precursor proteins on the outer surface of the organelle (22).

Although proteins destined for different mitochondrial compartments are imported by several different pathways, most or all of them traverse the outer membrane via the TOM complex. Transit through the TOM complex is sufficient for import of some outer membrane proteins, and of intermembrane space (IMS) proteins that are imported by a "folded trap" mechanism. In this mechanism, after the imported protein enters the IMS, intramolecular disulfide bonds form that lock it in a folded conformation and prevent its movement back out to the cytosol. Other types of incoming proteins are directed to other complexes after exiting the TOM complex. Incoming beta-barrel proteins are transferred to the SAM/TOB complex of the outer membrane, in a process involving the small TIM protein complexes of the IMS (Tim8p-Tim13p and Tim9p-Tim10p), and then inserted into the outer membrane. Matrix proteins and some inner membrane proteins are imported through the TOM complex and then the inner membrane TIM23 complex, which interact to form a supercomplex (6). Other inner membrane proteins are imported via the TOM complex and escorted across the IMS by the small TIM proteins to the inner membrane TIM22 complex, which mediates their integration into the inner membrane.

About TOM40

Tom40p is the main structural component of the channel that provides an aqueous pore across the hydrophobic membrane through which the imported preproteins are transported. It is an integral membrane protein embedded in the outer membrane, with beta-sheet strands predicted to form a beta-barrel structure around a pore of 0.2 nm in diameter (23, 24). In addition, Tom40p functions as a chaperone, keeping the preproteins in an unfolded conformation during their translocation (25). The other components of the pore, Tom5p, Tom6p, and Tom7p, associate with Tom40p and appear to play stabilizing roles (24). Tom40p is the only essential component of the TOM complex and the tom40 null mutation is unconditionally lethal (26).

Last updated: 2009-03-17 Contact SGD

References cited on this page View Complete Literature Guide for TOM40
1) Pfanner N, et al.  (1996) Uniform nomenclature for the protein transport machinery of the mitochondrial membranes. Trends Biochem Sci 21(2):51-2
2) Vestweber D, et al.  (1989) A 42K outer-membrane protein is a component of the yeast mitochondrial protein import site. Nature 341(6239):205-9
3) Meisinger C, et al.  (1999) The preprotein translocase of the outer mitochondrial membrane: receptors and a general import pore. Cell Mol Life Sci 56(9-10):817-24
4) Rapaport D and Neupert W  (1999) Biogenesis of Tom40, core component of the TOM complex of mitochondria. J Cell Biol 146(2):321-31
5) Ryan MT, et al.  (2000) The transport machinery for the import of preproteins across the outer mitochondrial membrane. Int J Biochem Cell Biol 32(1):13-21
6) Chacinska A, et al.  (2003) Mitochondrial translocation contact sites: separation of dynamic and stabilizing elements in formation of a TOM-TIM-preprotein supercomplex. EMBO J 22(20):5370-81
7) Pfanner N, et al.  (2004) Assembling the mitochondrial outer membrane. Nat Struct Mol Biol 11(11):1044-8
8) Rao S, et al.  (2012) Biogenesis of the preprotein translocase of the outer mitochondrial membrane: protein kinase A phosphorylates the precursor of Tom40 and impairs its import. Mol Biol Cell 23(9):1618-27
9) Neupert W and Herrmann JM  (2007) Translocation of proteins into mitochondria. Annu Rev Biochem 76:723-49
10) Mokranjac D and Neupert W  (2009) Thirty years of protein translocation into mitochondria: unexpectedly complex and still puzzling. Biochim Biophys Acta 1793(1):33-41
11) Moczko M, et al.  (1992) Identification of the mitochondrial receptor complex in Saccharomyces cerevisiae. FEBS Lett 310(3):265-8
12) Dekker PJ, et al.  (1998) Preprotein translocase of the outer mitochondrial membrane: molecular dissection and assembly of the general import pore complex. Mol Cell Biol 18(11):6515-24
13) Wu Y and Sha B  (2006) Crystal structure of yeast mitochondrial outer membrane translocon member Tom70p. Nat Struct Mol Biol 13(7):589-93
14) Muto T, et al.  (2001) NMR identification of the Tom20 binding segment in mitochondrial presequences. J Mol Biol 306(2):137-43
15) Young JC, et al.  (2003) Molecular chaperones Hsp90 and Hsp70 deliver preproteins to the mitochondrial import receptor Tom70. Cell 112(1):41-50
16) Allen R, et al.  (2002) A conserved proline residue is present in the transmembrane-spanning domain of Tom7 and other tail-anchored protein subunits of the TOM translocase. FEBS Lett 514(2-3):347-50
17) Becker L, et al.  (2005) Preprotein translocase of the outer mitochondrial membrane: reconstituted Tom40 forms a characteristic TOM pore. J Mol Biol 353(5):1011-20
18) Wiedemann N, et al.  (2004) Biogenesis of the protein import channel Tom40 of the mitochondrial outer membrane: intermembrane space components are involved in an early stage of the assembly pathway. J Biol Chem 279(18):18188-94
19) Kunkele KP, et al.  (1998) The isolated complex of the translocase of the outer membrane of mitochondria. Characterization of the cation-selective and voltage-gated preprotein-conducting pore. J Biol Chem 273(47):31032-9
20) Dietmeier K, et al.  (1997) Tom5 functionally links mitochondrial preprotein receptors to the general import pore. Nature 388(6638):195-200
21) Honlinger A, et al.  (1996) Tom7 modulates the dynamics of the mitochondrial outer membrane translocase and plays a pathway-related role in protein import. EMBO J 15(9):2125-37
22) van Wilpe S, et al.  (1999) Tom22 is a multifunctional organizer of the mitochondrial preprotein translocase. Nature 401(6752):485-9
23) Hill K, et al.  (1998) Tom40 forms the hydrophilic channel of the mitochondrial import pore for preproteins [see comment] Nature 395(6701):516-21
24) Model K, et al.  (2002) Protein translocase of the outer mitochondrial membrane: role of import receptors in the structural organization of the TOM complex. J Mol Biol 316(3):657-66
25) Esaki M, et al.  (2003) Tom40 protein import channel binds to non-native proteins and prevents their aggregation. Nat Struct Biol 10(12):988-94
26) Baker KP, et al.  (1990) A yeast mitochondrial outer membrane protein essential for protein import and cell viability. Nature 348(6302):605-9