COPI vesicles

Gene Ontology
Parent
Golgi-associated vesicle barbed border vesicle
Subordinate
Golgi ER transport vesicle. Inter Golgi transport vesicle
QuickGO

COPI ( English coat protein complex I , coat-protein complex I ') are transport vesicles in eukaryotic cells . They are used to transport lipids and extracellular proteins from the cis side of the Golgi apparatus in the direction of the endoplasmic reticulum (ER), which is also referred to as retrograde transport. In addition, newly synthesized proteins from COPII vesicleswere transported to the cis side of the Golgi apparatus, transported with COPI vesicles via the Golgi cisterns to the trans side. Another function of the COPI vesicles is the “packaging” of the Golgi apparatus during mitosis .

Structure and mechanism of the transport vesicle

COPI vesicles are 50-100 nm in size and differ from COPII vesicles in their coat protein. The envelope protein, the so-called coatomer, consists of seven different subunits. The coatomer consists of a trimer complex of α / β '/ ε-COP and a tetramer of β / γ / ζ / δ-COP. Furthermore, a COPI vesicle requires the adenosyl-ribosylation factor 1 (ARF1), which is present in the "inactive" form with GDP. The guanine nucleotide exchange factor for Arf1 (ARF-GEF) is required for activation or GDP / GTP exchange . There must be dimers in the membrane for the p23 / p24 protein . ARF1-GTP binds to the p24 transmembrane proteins . Once this has happened, the coatomer can bind to ARF1-GTP, p23 / p24 and the cargo protein. The coatomer also ensures that tension builds up in the membrane, so that the membrane deforms into a ball until the tension in the membrane is so high that it only relaxes via the constriction of the Cis-Golgi membrane can. With the protein envelope around the vesicle, however, no fusion with the target membrane can take place; this requires the hydrolysis of GTP to GDP at ARF1 with the help of the GTPase-activating protein (ARF-GAF).

The binding of luminal proteins to be transported takes place via the KDEL receptor protein. This protein binds to the coatomer as well as to the protein to be transported and ensures the transport from the lumen of the Golgi apparatus to the ER. The protein must contain the signal peptide KDEL (this stands for lysine , aspartic acid , glutamic acid , leucine , see amino acid code ). In the ER, the KDEL receptor and protein dissociate, presumably due to the pH difference between the ER and the Golgi apparatus. In contrast, transmembrane proteins that are to be transported to the endoplasmic reticulum can be recognized by the dilysine sorting signal (KKXX) in the area of the cytosolic tail.

Individual evidence

^ Vincent Popoff, Frank Adolf, Britta Brügger, Felix Wieland: COPI Budding within the Golgi Stack. In: Cold Spring Harb Perspect Biol. 3, 2011, pp. A005231 doi: 10.1101 / cshperspect.a005231
^ F. Letourneur, EC Gaynor, S. Hennecke, C. Démollière, R. Duden, SD Emr et al .: Coatomer is essential for retrieval of dilysine-tagged proteins to the endoplasmic reticulum. In: Cell. 79 (7), 1994, pp. 1199-207. doi: 10.1016 / 0092-8674 (94) 90011-6 . PMID 8001155

[1] Vincent Popoff, Frank Adolf, Britta Brügger, Felix Wieland: COPI Budding within the Golgi Stack. In: Cold Spring Harb Perspect Biol. 3, 2011, pp. A005231 doi: 10.1101 / cshperspect.a005231

[2] F. Letourneur, EC Gaynor, S. Hennecke, C. Démollière, R. Duden, SD Emr et al .: Coatomer is essential for retrieval of dilysine-tagged proteins to the endoplasmic reticulum. In: Cell. 79 (7), 1994, pp. 1199-207. doi: 10.1016 / 0092-8674 (94) 90011-6 . PMID 8001155