COPII (Coat Protein Complex II) is a group of proteins that facilitate the formation of vesicles responsible for transporting proteins from the endoplasmic reticulum (ER) to the Golgi apparatus or the ER-Golgi intermediate compartment. This transport process is called anterograde transport, meaning it moves forward from the ER towards the Golgi. COPII assembles in two layers: an inner layer composed of proteins Sar1, Sec23, and Sec24, and an outer lattice formed by Sec13 and Sec31. It is essential for selectively packaging and exporting newly synthesized proteins from the ER for further processing in the Golgi apparatus.
In summary:
- COPII is involved in the anterograde (forward) transport from the rough ER to the cis-Golgi.
- It helps form vesicles that carry cargo proteins out of the ER.
- COPII assembly is initiated by the activation of Sar1, which leads to the recruitment of other coat proteins that form the vesicle coat.
This contrasts with COPI, which mediates retrograde transport, moving proteins backward from the Golgi to the ER.
