Synthesized proteins are primarily transferred from the endoplasmic reticulum (ER) to the Golgi apparatus via transport vesicles.
Here's a breakdown of the process:
- ER Export: Proteins synthesized in the ER (specifically the rough ER) and destined for the Golgi, lysosomes, plasma membrane, or secretion are packaged into transport vesicles. These vesicles bud off from specialized regions of the ER membrane.
- Vesicle Formation: The formation of these vesicles involves coat proteins, notably COPII (Coat Protein Complex II), which help to deform the ER membrane and select the cargo proteins for packaging.
- ERGIC Transit: The transport vesicles bud from the ER membrane and then fuse with each other, forming vesicular tubular clusters. These clusters move along microtubules to form the ER-Golgi intermediate compartment (ERGIC), a distinct compartment located between the ER and the Golgi. The ERGIC functions as a sorting station.
- Golgi Arrival: From the ERGIC, transport vesicles bud again, carrying the selected proteins to the cis-Golgi network (CGN), the entry point to the Golgi apparatus. These vesicles fuse with the CGN membrane, delivering their protein cargo.
In summary, the journey of synthesized proteins involves:
- Packaging into transport vesicles in the ER.
- Fusion of ER-derived vesicles to form ERGIC.
- Transport from the ERGIC to the Golgi via further transport vesicles.
- Fusion with the Golgi membrane and release of proteins within the Golgi lumen.
This vesicle-mediated transport ensures that proteins are correctly delivered to their final destinations within the cell or outside of it.
