endoplasmic reticulum to Golgi vesicle-mediated transport

Definition

Target type: biologicalprocess

The directed movement of substances from the endoplasmic reticulum (ER) to the Golgi, mediated by COP II vesicles. Small COP II coated vesicles form from the ER and then fuse directly with the cis-Golgi. Larger structures are transported along microtubules to the cis-Golgi. [GOC:ascb_2009, GOC:dph, GOC:jp, GOC:tb, ISBN:0716731363]

The endoplasmic reticulum (ER) to Golgi vesicle-mediated transport is a crucial process in eukaryotic cells, responsible for the movement of newly synthesized proteins and lipids from the ER to the Golgi apparatus. This complex pathway involves multiple steps and a diverse cast of molecular players, including proteins, lipids, and small GTPases.

**1. Budding from the ER:** The journey begins at the ER, where proteins destined for the Golgi are packaged into transport vesicles. These vesicles form by a process called budding, which is initiated by the recruitment of coat proteins to the ER membrane. The primary coat protein involved in ER-to-Golgi transport is COPII, a complex of four proteins: Sec23, Sec24, Sec13, and Sec31. COPII proteins assemble into a cage-like structure around the budding vesicle, providing structural support and facilitating cargo selection.

**2. Cargo Selection:** The COPII coat plays a critical role in cargo selection, ensuring that only the appropriate proteins and lipids are packaged into the vesicles. This selectivity is achieved through interactions between the coat proteins and specific sorting signals present on the cargo molecules. These signals, often short peptide sequences, are recognized by the Sec24 subunit of the COPII coat, which acts as a cargo adaptor.

**3. Vesicle Formation and Release:** Once the cargo is loaded and the COPII coat is assembled, the vesicle membrane begins to pinch off from the ER. This process involves the recruitment of other proteins, including the GTPase Sar1, which provides the energy required for membrane deformation. Sar1 also helps to recruit other proteins that facilitate vesicle scission and release.

**4. Vesicle Transport:** Once released from the ER, the transport vesicles move towards the Golgi apparatus. This movement is facilitated by microtubules, which act as tracks for the vesicles, and motor proteins, such as dynein and kinesin, which provide the force for vesicle movement.

**5. Fusion with the Golgi:** The final step in the journey involves the fusion of the transport vesicle with the Golgi membrane. This process is mediated by a complex of proteins known as SNAREs. SNAREs are transmembrane proteins that reside on both the vesicle and the target membrane. These proteins interact with each other, bringing the two membranes into close proximity and ultimately triggering their fusion.

**6. Golgi Processing:** Once inside the Golgi, the cargo undergoes further processing and modification. The Golgi apparatus is composed of a series of flattened, membrane-enclosed sacs called cisternae, each with a distinct set of enzymes. As the cargo moves through these compartments, it undergoes glycosylation, phosphorylation, and other modifications that prepare it for its final destination.

**7. Sorting and Delivery:** Finally, the modified proteins and lipids are sorted and packaged into new vesicles, which bud off from the trans-Golgi network (TGN). These vesicles then travel to their final destinations, including the plasma membrane, lysosomes, or other organelles.'
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Proteins (3)

Compounds (9)