Summary: Coatomer (COPI) alpha subunit C-terminus
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|COPI C-terminal domain|
COPI is a protein complex 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.
 Coat proteins
Coat protein, or COPI, is an ADP ribosylation factor (ARF)-dependent adaptor protein involved in membrane traffic. COPI was first identified in retrograde traffic from the cis-Golgi to the rough endoplasmic reticulum (ER) and is the most extensively studied of ARF-dependent adaptors. COPI consists of seven subunits which compose the heptameric protein complex.
The primary function of adaptors is the selection of cargo proteins for their incorporation into nascent carriers. In the case of the adaptor COPI, cargo containing the sorting motif KKXX interact with COPI to form carriers which are transported from the cis-Golgi to the rough ER. 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 30 mammalian ARFs, and 29 in humans due to the loss of ARF2. 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 guanine nucleotide exchange factors (GEFs) and ARF GTPase activating proteins (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. 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.
- 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, which interact with COPI. 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.
- Coat Protein Complex I at the US National Library of Medicine Medical Subject Headings (MeSH)
- 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.
- Schekman R., Orci L. (1996). "Coat proteins and vesicle budding". Science 271 (5255): 1526–1533. doi:10.1126/science.271.5255.1526. PMID 8599108.
- 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.
- 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.
- 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. //www.ncbi.nlm.nih.gov/pmc/articles/PMC2121093/.
- 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. //www.ncbi.nlm.nih.gov/pmc/articles/PMC2120996/.
- 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.
 See also
- COPII vesicles
- Clathrin vesicles
- Glyceraldehyde 3-phosphate dehydrogenase#ER_to_Golgi_transport
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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 . Note that many family members also contain the PF04053 domain.
External database links
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.
More information about these proteins can be found at Protein of the Month: Clathrin [PUBMED:].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||COPI vesicle coat (GO:0030126)|
|Molecular function||protein binding (GO:0005515)|
|structural molecule activity (GO:0005198)|
|Biological process||intracellular protein transport (GO:0006886)|
|vesicle-mediated transport (GO:0016192)|
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|Seed source:||Pfam-B_20121 (release 10.0)|
|Author:||Vella Briffa B|
|Number in seed:||5|
|Number in full:||402|
|Average length of the domain:||362.60 aa|
|Average identity of full alignment:||35 %|
|Average coverage of the sequence by the domain:||33.49 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||6|
|Download:||download the raw HMM for this family|
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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 10 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 seqence.
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