COPII vesicles

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

COPII vesicle ( engl. Coat protein complex II =, coat-protein complex II ') are usually 50 to 90 nm-sized transport vesicles in eukaryotic cells . They serve the secretory anterograde (downstream) transport of biomolecules within the cell. However, their size can grow up to 300 to 400 nm to allow the transport of procollagen fibers . The COPII transport starts here from the rough endoplasmic reticulum (rER), in which vesicles form at so-called ER exit sites (ERES) and thus cargo molecules are enclosed or attached to the protein-membrane complex. Lipids , signal molecules or newly synthesized proteins can be transported as cargo molecules to the tubular endoplasmic-reticulum-Golgi-intercompartment (ERGIC). The ERGIC is located in the cell between the ER and the cis side of the Golgi apparatus .

COPII vesicle structure

COPII vesicles consist of five protein subunits and the ER membrane from the ERES. The proteins form an inner and an outer shell around the ER double-layer membrane. The inner shell includes the proteins Sec23 and Sec24, which in combination with the small GTPase Sar1a can attach to the ER membrane. There are two isoforms A and B of the Sec23 subunit in eukaryotic cells. The Sec24 subunit exists in four different isoforms A, B, C and D. The outer protein shell is composed of the two proteins Sec13 and Sec31. Sec31 occurs in the two isoforms A and B. This structure is analogous in yeast, but there are differences in the amino acid sequences . In yeast the proteins Sec23p / Sec24p and Sec13p / Sec31p are called.

COPII vesicle budding

To initiate the formation of a vesicle bud, Sar1a must first be loaded with GTP . The transmembrane protein Sec12 is required for this, which catalyzes the GDP / GTP exchange at Sar1a. If Sar1a is bound to the ER membrane, the heterodimeric subunit of Sec23 / Sec24 is attached to the GTPase. After the inner shell has formed, the heterotetrameric complex of Sec13 / Sec31 can attach to the inner shell. This process continues until a vesicle bud has formed and a COPII vesicle becomes detached from the ERES. In this process, the Sec24 subunit is important for the selective uptake of cargo. The different isoforms of Sec24 have different protein sequence motifs that are responsible for binding the cargo molecules.

See also

Individual evidence

  1. ↑ T. Szul, E. Sztul: COPII and COPI traffic at the ER-Golgi interface. In: Physiology (Bethesda, Md.). 26 (5), 2011, pp. 348-364. doi: 10.1152 / physiol.00017.2011
  2. ↑ L. Jin, KB Pahuja, KE Wickliffe, A. Gorur, C. Baumgärtel, R. Schekman, M. Rape: Ubiquitin-dependent regulation of COPII coat size and function. In: Nature. 482 (7386), 2012, pp. 495-500. doi: 10.1038 / nature10822
  3. ^ C. Barlowe, L. Orci, T. Yeung, M. Hosobuchi, S. Hamamoto, N. Salama, MF Rexach et al: COPII: a membrane coat formed by Sec proteins that drive vesicle budding from the endoplasmic reticulum. In: Cell. 77 (6), 1994, pp. 895-907. Retrieved from PMID 8004676
  4. ↑ A. Schweizer, JA Fransen, K. Matter, TE Kreis, L. Ginsel, HP Hauri: Identification of an intermediate compartment involved in protein transport from endoplasmic reticulum to Golgi apparatus. In: European journal of cell biology. 53 (2), 1990, pp. 185-196. Department of Pharmacology, University of Basel, Switzerland.
  5. ↑ T. Szul, E. Sztul: COPII and COPI traffic at the ER-Golgi interface. In: Physiology (Bethesda, Md.). 26 (5), 2011, pp. 348-364. doi: 10.1152 / physiol.00017.2011

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