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1  structure 235  species 0  interactions 1056  sequences 37  architectures

Family: TOM20_plant (PF06552)

Summary: Plant specific mitochondrial import receptor subunit TOM20

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This is the Wikipedia entry entitled "Translocase of the outer membrane". More...

Translocase of the outer membrane Edit Wikipedia article

Mitochondrial import receptor subunit TOM20
PBB Protein TOMM20 image.jpg
OPM superfamily266
OPM protein3awr
TOM7 family
Mitochondrial import receptor subunit Tom22

The translocase of the outer membrane (TOM) is a complex of proteins found in the outer mitochondrial membrane of the mitochondria. It allows movement of proteins through this barrier and into the intermembrane space of the mitochondrion. Most of the proteins needed for mitochondrial function are encoded by the nucleus of the cell. The outer membrane of the mitochondrion is impermeable to large molecules greater than 5000 Daltons.[1] The TOM works in conjunction with the translocase of the inner membrane (TIM) to translocate proteins into the mitochondrion. Many of the proteins in the TOM complex, such as TOMM22, were first identified in Neurospora crassa and Saccharomyces cerevisiae.[2]

The complete mitochondrial protein translocase complex includes at least 19 proteins: several chaperones, four proteins of the outer membrane translocase (Tom) import receptor, five proteins of the Tom channel complex, five proteins of the inner membrane translocase (Tim) and three "motor" proteins.

Protein targeting to the mitochondria

There are various mitochondrial import pathways that exist to facilitate the import of precursor proteins to their destined mitochondrial subcompartments. HSP90 aids the delivery of the mitochondrial preprotein to the TOM complex in an ATP-dependent process.[3] Many precursor proteins (those that are destined for the matrix) contain amino-terminal presequences that carry information required for the targeting of proteins to the mitochondrial matrix[4] These matrix targeting signals generally contain 10-80 amino acid residues that take on the conformation of an amphipathic-α helix[5] and contain one positive and hydrophobic face. Once the precursor reaches the matrix, the presequence is typically cleaved off by the matrix processing peptidase.[6] Proteins targeted to other sub-compartments of the mitochondria such as the intermembrane space and inner mitochondrial membrane, contain internal targeting signals, these signals have an indefinable nature and are inconsistent in their pattern. Proteins targeted to the outer membrane also contain internal targeting signals, not all of which have been identified, and include proteins that take on a β-barrel structure,[7] such as Tom40. Some proteins however, that are targeted to the outer mitochondrial membrane contain a hydrophobic tail domain that anchors the protein to the membrane.[8]

Members of the complex

The translocase of the outer membrane (TOM) forms a complex made of Tom70, Tom22, and Tom20, along with Tom40, Tom7, Tom6, and Tom5. Tom20 and Tom22 are preprotein receptors, which are responsible for recognition of the cleavable presequence possessed by mitochondrial-targeted proteins.[9] Tom70 is also a preprotein receptor and may recognise some cleavable presequence proteins, however it is mainly responsible for the recognition of non-cleavable preproteins and acts as a point for chaperone binding.[6][10] Tom22 is anchored to the outer membrane by a single transmembrane segment and also plays a role in stabilizing the TOM complex.[11] Tom40 is the core element of the translocase complex and complexes with Tom22 with a mass of approximately 350k Daltons.[12] It forms the central protein-conducting channel with a diameter of approximately 2.5 nm.[12] The human Tom22 is approximately 15.5k Daltons and complexes with Tom20.[13] The N-terminal end of Tom22 extends into the cytosol and is involved in preprotein binding.[13]

Human proteins


See also


  1. ^ Alberts, Bruce; Alexander Johnson; Julian Lewis; Martin Raff; Keith Roberts; Peter Walter (1994). Molecular Biology of the Cell. New York: Garland Publishing Inc. ISBN 978-0-8153-3218-3.
  2. ^ Seki N, Moczko M, Nagase T, et al. (1996). "A human homolog of the mitochondrial protein import receptor Mom19 can assemble with the yeast mitochondrial receptor complex". FEBS Lett. 375 (3): 307–10. doi:10.1016/0014-5793(95)01229-8. PMID 7498524.
  3. ^ Humphries AD, Streimann IC, Stojanovski D, Johnston AJ, Yano M, Hoogenraad NJ, Ryan MT (March 2005). "Dissection of the mitochondrial import and assembly pathway for human Tom40". J Biol Chem. 280 (12): 11535–43. doi:10.1074/jbc.M413816200. PMID 15644312.
  4. ^ Saitoh T, Igura M, Obita T, Ose T, Kojima R, Maenaka K, Endo T, Kohda D (November 2007). "Tom20 recognizes mitochondrial presequences through dynamic equilibrium among multiple bound states". EMBO J. 26 (22): 4777–87. doi:10.1038/sj.emboj.7601888. PMC 2080804. PMID 17948058.
  5. ^ Tokatlidis K, Vial S, Luciano P, Vergnolle M, Clémence S (2000). "Membrane protein import in yeast mitochondria". Biochem. Soc. Trans. 28 (4): 495–9. doi:10.1042/0300-5127:0280495. PMID 10961947.
  6. ^ a b Young JC, Hoogenraad NJ, Hartl FU (January 2003). "Molecular chaperones Hsp90 and Hsp70 deliver preproteins to the mitochondrial import receptor Tom70". Cell. 112 (1): 41–50. doi:10.1016/S0092-8674(02)01250-3. PMID 12526792.
  7. ^ Bolender N, Sickmann A, Wagner R, Meisinger C, Pfanner N (January 2008). "Multiple pathways for sorting mitochondrial precursor proteins". EMBO Rep. 9 (1): 42–9. doi:10.1038/sj.embor.7401126. PMC 2246611. PMID 18174896.
  8. ^ Koehler CM, Merchant S, Schatz G (November 1999). "How membrane proteins travel across the mitochondrial intermembrane space". Trends Biochem. Sci. 24 (11): 428–32. doi:10.1016/S0968-0004(99)01462-0. PMID 10542408.
  9. ^ Ryan MT, Müller H, Pfanner N (July 1999). "Functional staging of ADP/ATP carrier translocation across the outer mitochondrial membrane". J. Biol. Chem. 274 (29): 20619–27. doi:10.1074/jbc.274.29.20619. PMID 10400693.
  10. ^ Asai T, Takahashi T, Esaki M, Nishikawa S, Ohtsuka K, Nakai M, Endo T (May 2004). "Reinvestigation of the requirement of cytosolic ATP for mitochondrial protein import". J. Biol. Chem. 279 (19): 19464–70. doi:10.1074/jbc.M401291200. PMID 15001571.
  11. ^ Endres M, Neupert W, Brunner M (June 1999). "Transport of the ADP/ATP carrier of mitochondria from the TOM complex to the TIM22.54 complex". EMBO J. 18 (12): 3214–21. doi:10.1093/emboj/18.12.3214. PMC 1171402. PMID 10369662.
  12. ^ a b Ahting U, Thieffry M, Engelhardt H, Hegerl R, Neupert W, Nussberger S (2001). "Tom40, the Pore-Forming Component of the Protein-Conducting Tom Channel in the Outer Membrane of Mitochondria". J. Cell Biol. 153 (6): 1151–60. doi:10.1083/jcb.153.6.1151. PMC 2192023. PMID 11402060.
  13. ^ a b Yano M, Hoogenraad N, Terada K, Mori M (2000). "Identification and Functional Analysis of Human Tom22 for Protein Import into Mitochondria". Mol Cell Biol. 20 (19): 7205–13. doi:10.1128/MCB.20.19.7205-7213.2000. PMC 86274. PMID 10982837.

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This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.

Plant specific mitochondrial import receptor subunit TOM20 Provide feedback

This family consists of several plant specific mitochondrial import receptor subunit TOM20 (translocase of outer membrane 20 kDa subunit) proteins. Most mitochondrial proteins are encoded by the nuclear genome, and are synthesised in the cytosol. TOM20 is a general import receptor that binds to mitochondrial pre-sequences in the early step of protein import into the mitochondria [1].

Literature references

  1. Obita T, Muto T, Endo T, Kohda D; , J Mol Biol 2003;328:495-504.: Peptide library approach with a disulfide tether to refine the Tom20 recognition motif in mitochondrial presequences. PUBMED:12691756 EPMC:12691756

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External database links

This tab holds annotation information from the InterPro database.

No InterPro data for this Pfam family.

Domain organisation

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Pfam Clan

This family is a member of clan TPR (CL0020), which has the following description:

Tetratricopeptide-like repeats are found in a numerous and diverse proteins involved in such functions as cell cycle regulation, transcriptional control, mitochondrial and peroxisomal protein transport, neurogenesis and protein folding.

The clan contains the following 176 members:

Adaptin_N Alkyl_sulf_dimr ANAPC3 ANAPC5 ANAPC8 APC_rep API5 Arm Arm_2 Arm_3 Arm_vescicular Atx10homo_assoc B56 BAF250_C BTAD CAS_CSE1 ChAPs CHIP_TPR_N CID CLASP_N Clathrin Clathrin-link Clathrin_H_link Clathrin_propel Cnd1 Cnd3 Coatomer_E Cohesin_HEAT Cohesin_load ComR_TPR COPI_C CPL CRM1_C CRM1_repeat CRM1_repeat_3 Cse1 CTK3 DHR-2 DIL DNA_alkylation Dopey_N Drf_FH3 Drf_GBD DUF1822 DUF2019 DUF2225 DUF3385 DUF3458_C DUF3808 DUF3856 DUF4042 DUF5588 DUF5691 DUF6340 DUF6377 DUF924 EAD11 EST1 EST1_DNA_bind FAT Fis1_TPR_C Fis1_TPR_N Foie-gras_1 GUN4_N HAT HEAT HEAT_2 HEAT_EZ HEAT_PBS HEAT_UF HemY_N HrpB1_HrpK HSM3_C HSM3_N IBB IBN_N IFRD Importin_rep Importin_rep_2 Importin_rep_3 Importin_rep_4 Importin_rep_5 Importin_rep_6 Insc_C KAP Leuk-A4-hydro_C LRV LRV_FeS MA3 MIF4G MIF4G_like MIF4G_like_2 MMS19_C Mo25 MRP-S27 Mtf2 NARP1 Neurochondrin Nipped-B_C Nro1 NSF Paf67 ParcG PC_rep PHAT PI3Ka PknG_TPR PPP5 PPR PPR_1 PPR_2 PPR_3 PPR_long PPTA Proteasom_PSMB PUF Rapsyn_N RIX1 RNPP_C RPM2 RPN7 Sel1 SHNi-TPR SNAP SPO22 SRP_TPR_like ST7 Suf SusD-like SusD-like_2 SusD-like_3 SusD_RagB SYCP2_ARLD TAF6_C TAL_effector TAtT Tcf25 TIP120 TOM20_plant TPR_1 TPR_10 TPR_11 TPR_12 TPR_14 TPR_15 TPR_16 TPR_17 TPR_18 TPR_19 TPR_2 TPR_20 TPR_21 TPR_22 TPR_3 TPR_4 TPR_5 TPR_6 TPR_7 TPR_8 TPR_9 TPR_MalT TTC7_N UNC45-central Upf2 V-ATPase_H_C V-ATPase_H_N Vac14_Fab1_bd Vitellogenin_N Vps39_1 W2 WSLR Wzy_C_2 Xpo1 YcaO_C YfiO Zmiz1_N


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Curation View help on the curation process

Seed source: Pfam-B_17991 (release 10.0)
Previous IDs: none
Type: Repeat
Sequence Ontology: SO:0001068
Author: Moxon SJ
Number in seed: 5
Number in full: 1056
Average length of the domain: 136.00 aa
Average identity of full alignment: 30 %
Average coverage of the sequence by the domain: 51.43 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 57096847 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 20.6 20.6
Trusted cut-off 20.6 20.6
Noise cut-off 20.5 20.5
Model length: 187
Family (HMM) version: 14
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For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the TOM20_plant domain has been found. There are 1 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein sequence.

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