COPI
| COPI C-terminal domain | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | COPI_C | ||||||||
| Pfam | PF06957 | ||||||||
| InterPro | IPR010714 | ||||||||
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| Available protein structures: | |
|---|---|
| Pfam | structures |
| PDB | RCSB PDB; PDBe; PDBj |
| PDBsum | structure summary |
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, namely α, β, β', γ, δ, ε and ζ.
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.
ADP ribosylation factor (ARF) is a GTPase involved in membrane traffic. There are 6 mammalian ARFs which are regulated by over 30 GEFs and 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 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.
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