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22  structures 1369  species 0  interactions 2181  sequences 86  architectures

Family: COPI_C (PF06957)

Summary: Coatomer (COPI) alpha subunit C-terminus

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This is the Wikipedia entry entitled "COPI". More...

COPI Edit Wikipedia article

Electron micrograph of in vitro–formed COPI-coated vesicles. Average vesicle diameter at the membrane level is 60 nm.

COPI is a coatomer, a protein complex[1] that coats vesicles transporting proteins from the cis end of the Golgi complex back to the rough endoplasmic reticulum (ER), where they were originally synthesized, and between Golgi compartments. This type of transport is termed as retrograde transport, in contrast to the anterograde transport associated with the COPII protein. The name "COPI" refers to the specific coat protein complex that initiates the budding process on the cis-Golgi membrane. The coat consists of large protein subcomplexes that are made of seven different protein subunits, namely α, β, β', γ, δ, ε and ζ.


Coat proteins

Coat protein, or COPI, is an ADP ribosylation factor (ARF)-dependent protein involved in membrane traffic.[2] COPI was first identified in retrograde traffic from the cis-Golgi to the rough endoplasmic reticulum (ER)[3][4] and is the most extensively studied of ARF-dependent adaptors. COPI consists of seven subunits which compose the heteroheptameric protein complex.

The primary function of adaptors is the selection of cargo proteins for their incorporation into nascent carriers. Cargo containing the sorting motifs KKXX and KXKXX interact with COPI to form carriers which are transported from the cis-Golgi to the ER.[5][6][7][8][9] Current views suggest that ARFs are also involved in the selection of cargo for incorporation into carriers.

Budding process

ADP ribosylation factor (ARF) is a GTPase involved in membrane traffic. There are 6 mammalian ARFs which are regulated by over 30 Guanine Nucleotide Exchange Factors(GEFs) and GTPase activating proteins(GAPs). ARF is post-translationally modified at the N-terminus by the addition of the fatty acid myristate.

ARF cycles between GTP and GDP-bound conformations. In the GTP-bound form, ARF conformation changes such that the myristate and hydrophobic N-terminal become more exposed and associate with the membrane. The interconversion between GTP and GDP bound states is mediated by ARF GEFs and ARF GAPs. At the membrane, ARF-GTP is hydrolyzed to ARF-GDP by ARF GAPs. Once in the GDP-bound conformation, ARF converts to a less hydrophobic conformation and dissociates from the membrane. Soluble ARF-GDP is converted back to ARF-GTP by GEFs.

1. Luminal proteins: Proteins found in the lumen of the Golgi complex that need to be transported to the lumen of the ER contain the signal peptide KDEL.[10] This sequence is recognized by a membrane-bound KDEL receptor. In yeast, this is ERD2P and in mammals it is KDELR. This receptor then binds to an ARF-GEF, a class of guanine nucleotide exchange factors. This protein in turn binds to the ARF. This interaction causes ARF to exchange its bound GDP for GTP. Once this exchange is made ARF binds to the cytosolic side of the cis-Golgi membrane and inserts the myristoylated N-terminal amphipathic alpha-helix into the membrane.[11]
2. Membrane proteins: Transmembrane proteins which reside in the ER contain sorting signals in their cytosolic tails which direct the protein to exit the Golgi and return to the ER. These sorting signals, or motifs, typically contain the amino acid sequence KKXX or KXKXX, which interact with COPI subunits α-COP and β'-COP.[10][9] The order in which adaptor proteins associate with cargo, or adaptor proteins associate with ARFs is unclear, however, in order to form a mature transport carrier coat protein, adaptor, cargo, and ARF must all associate.

Membrane deformation and carrier budding occurs following the collection of interactions described above. The carrier then buds off of the donor membrane, in the case of COPI this membrane is the cis-Golgi, and the carrier moves to the ER where it fuses with the acceptor membrane and its content is expelled.


The COPI triad. Color scheme: membrane - gray; Arf1 - pink; gamma-COP - light green; beta-COP, dark green; zeta-COP - yellow; delta-COP - orange; betaprime-COP - light blue; alpha-COP - dark blue

On the surface of a vesicle COPI molecules form symmetric trimers ("triads"). The curved triad structure positions the Arf1 molecules and cargo binding sites proximal to the membrane. The β′- and α-COP subunits form an arch over the γζβδ-COP subcomplex, orienting their N-terminal domains such that the K(X)KXX cargo-motif binding sites are optimally positioned against the membrane. Thus β′- and α-COP do not form a cage or lattice as in COPII and clathrin coats as previously suggested;[12] instead, they are linked to one another via the γζβδ-COP subcomplexes, forming an interconnected assembly.[13] The triads are linked together with contacts of variable valence making up four different types of contacts.[14]

See also


  1. ^ Coat+Protein+Complex+I at the US National Library of Medicine Medical Subject Headings (MeSH)
  2. ^ Serafini T, Orci L, Amherdt M, Brunner M, Kahn RA, Rothman JE (1991). "ADP-ribosylation factor is a subunit of the coat of Golgi-derived COP-coated vesicles: a novel role for a GTP-binding protein". Cell. 67 (2): 239–53. doi:10.1016/0092-8674(91)90176-Y. PMID 1680566.
  3. ^ Schekman R, Orci L (1996). "Coat proteins and vesicle budding". Science. 271 (5255): 1526–1533. doi:10.1126/science.271.5255.1526. PMID 8599108.
  4. ^ Cosson P, Letourneur F (1997). "Coatomer (COPI)-coated vesicles: role in intracellular transport and protein sorting". Curr Opin Cell Biol. 9 (4): 484–7. doi:10.1016/S0955-0674(97)80023-3. PMID 9261053.
  5. ^ Letourneur F, Gaynor EC, Hennecke S, Démollière C, Duden R, Emr SD, et al. (1994). "Coatomer is essential for retrieval of dilysine-tagged proteins to the endoplasmic reticulum". Cell. 79 (7): 1199–207. doi:10.1016/0092-8674(94)90011-6. PMID 8001155.
  6. ^ Sohn K, Orci L, Ravazzola M, Amherdt M, Bremser M, Lottspeich F, et al. (1996). "A major transmembrane protein of Golgi-derived COPI-coated vesicles involved in coatomer binding". J Cell Biol. 135 (5): 1239–48. doi:10.1083/jcb.135.5.1239. PMC 2121093. PMID 8947548.
  7. ^ Sönnichsen B, Watson R, Clausen H, Misteli T, Warren G (1996). "Sorting by COP I-coated vesicles under interphase and mitotic conditions". J Cell Biol. 134 (6): 1411–25. doi:10.1083/jcb.134.6.1411. PMC 2120996. PMID 8830771.
  8. ^ Orci L, Stamnes M, Ravazzola M, Amherdt M, Perrelet A, Söllner TH, et al. (1997). "Bidirectional transport by distinct populations of COPI-coated vesicles". Cell. 90 (2): 335–49. doi:10.1016/S0092-8674(00)80341-4. PMID 9244307.
  9. ^ a b Ma, Wenfu; Goldberg, Jonathan (2013-04-03). "Rules for the recognition of dilysine retrieval motifs by coatomer". The EMBO Journal. 32 (7): 926–937. doi:10.1038/emboj.2013.41. ISSN 1460-2075. PMC 3616288. PMID 23481256.
  10. ^ a b Mariano Stornaiuolo; Lavinia V. Lotti; Nica Borgese; Maria-Rosaria Torrisi; Giovanna Mottola; Gianluca Martire & Stefano Bonatti (March 2003). "KDEL and KKXX Retrieval Signals Appended to the Same Reporter Protein Determine Different Trafficking between Endoplasmic Reticulum, Intermediate Compartment, and Golgi Complex". Molecular Biology of the Cell. 14 (3): 889–902. doi:10.1091/mbc.E02-08-0468. PMC 151567. PMID 12631711.
  11. ^ Goldberg, J. (1998-10-16). "Structural basis for activation of ARF GTPase: mechanisms of guanine nucleotide exchange and GTP-myristoyl switching". Cell. 95 (2): 237–248. doi:10.1016/s0092-8674(00)81754-7. ISSN 0092-8674. PMID 9790530.
  12. ^ Lee, Changwook; Goldberg, Jonathan (2010-07-09). "Structure of coatomer cage proteins and the relationship among COPI, COPII, and clathrin vesicle coats". Cell. 142 (1): 123–132. doi:10.1016/j.cell.2010.05.030. ISSN 1097-4172. PMC 2943847. PMID 20579721.
  13. ^ Dodonova, S. O.; Diestelkoetter-Bachert, P.; von Appen, A.; Hagen, W. J. H.; Beck, R.; Beck, M.; Wieland, F.; Briggs, J. a. G. (2015-07-10). "VESICULAR TRANSPORT. A structure of the COPI coat and the role of coat proteins in membrane vesicle assembly". Science. 349 (6244): 195–198. doi:10.1126/science.aab1121. ISSN 1095-9203. PMID 26160949.
  14. ^ Faini, Marco; Prinz, Simone; Beck, Rainer; Schorb, Martin; Riches, James D.; Bacia, Kirsten; Brügger, Britta; Wieland, Felix T.; Briggs, John A. G. (2012-06-15). "The structures of COPI-coated vesicles reveal alternate coatomer conformations and interactions" (PDF). Science. 336 (6087): 1451–1454. doi:10.1126/science.1221443. ISSN 1095-9203. PMID 22628556.

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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.

Coatomer (COPI) alpha subunit C-terminus Provide feedback

This family represents the C-terminus (approximately 500 residues) of the eukaryotic coatomer alpha subunit. Coatomer (COPI) is a large cytosolic protein complex which forms a coat around vesicles budding from the Golgi apparatus. Such coatomer-coated vesicles have been proposed to play a role in many distinct steps of intracellular transport [1]. Note that many family members also contain the PF04053 domain.

Literature references

  1. Cosson P, Letourneur F; , Curr Opin Cell Biol 1997;9:484-487.: Coatomer (COPI)-coated vesicles: role in intracellular transport and protein sorting. PUBMED:9261053 EPMC:9261053

  2. Hsia KC, Hoelz A;, Proc Natl Acad Sci U S A. 2010;107:11271-11276.: Crystal structure of alpha-COP in complex with epsilon-COP provides insight into the architecture of the COPI vesicular coat. PUBMED:20534429 EPMC:20534429

This tab holds annotation information from the InterPro database.

InterPro entry IPR010714

Proteins synthesised on the ribosome and processed in the endoplasmic reticulum are transported from the Golgi apparatus to the trans-Golgi network (TGN), and from there via small carrier vesicles to their final destination compartment. This traffic is bidirectional, to ensure that proteins required to form vesicles are recycled. Vesicles have specific coat proteins (such as clathrin or coatomer) that are important for cargo selection and direction of transfer [ PUBMED:15261670 ]. While clathrin mediates endocytic protein transport, and transport from ER to Golgi, coatomers primarily mediate intra-Golgi transport, as well as the reverse Golgi to ER transport of dilysine-tagged proteins [ PUBMED:14690497 ]. For example, the coatomer COP1 (coat protein complex 1) is responsible for reverse transport of recycled proteins from Golgi and pre-Golgi compartments back to the ER, while COPII buds vesicles from the ER to the Golgi [ PUBMED:11208122 ]. Coatomers reversibly associate with Golgi (non-clathrin-coated) vesicles to mediate protein transport and for budding from Golgi membranes [ PUBMED:17041781 ]. Activated small guanine triphosphatases (GTPases) attract coat proteins to specific membrane export sites, thereby linking coatomers to export cargos. As coat proteins polymerise, vesicles are formed and budded from membrane-bound organelles. Coatomer complexes also influence Golgi structural integrity, as well as the processing, activity, and endocytic recycling of LDL receptors. In mammals, coatomer complexes can only be recruited by membranes associated to ADP-ribosylation factors (ARFs), which are small GTP-binding proteins. Coatomer complexes are hetero-oligomers composed of at least an alpha, beta, beta', gamma, delta, epsilon and zeta subunits.

This entry represents the C terminus (approximately 500 residues) of the eukaryotic coatomer alpha subunit [ PUBMED:12893528 , PUBMED:9261053 ]. This domain is found along with the INTERPRO domain.

Gene Ontology

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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 and family details

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Curation View help on the curation process

Seed source: Pfam-B_20121 (release 10.0)
Previous IDs: none
Type: Repeat
Sequence Ontology: SO:0001068
Author: Vella Briffa B
Number in seed: 29
Number in full: 2181
Average length of the domain: 358.50 aa
Average identity of full alignment: 37 %
Average coverage of the sequence by the domain: 33.18 %

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 19.7 19.7
Trusted cut-off 19.7 19.7
Noise cut-off 19.6 19.6
Model length: 406
Family (HMM) version: 13
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Archea Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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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 COPI_C domain has been found. There are 22 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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