Pinching-off of Coated Vesicles

COPI and COPII vesicle buds spontaneously pinch off from the donor organelle membrane when the leaflets on either side of the budding patch fuse together. These vesicles can now transport the cargo to the target organelle.

Clathrin-coated vesicles require dynamin, a cytosolic GTP-binding protein, to pinch off the bud.

First, dynamin assembles as a helical collar around the neck of the invaginated coated bud.

Dynamin contains a phosphatidylinositol 4,5-bisphosphate or PIP-binding domain, which anchors the protein to the membrane, and GTPase domains that couple GTP hydrolysis with the contraction of dynamin.

The energy derived from GTP hydrolysis drives a conformational change in dynamin that stretches by twisting the helix at the neck until the bud pinches off the plasma membrane.

The pinch off triggers PIP phosphatase to deplete phosphatidylinositol 4,5- bisphosphate from the vesicle membrane. This weakens the binding of adaptor protein to the membrane and destabilizes the clathrin coat.

The chaperone protein Hsp70 and its co-chaperone auxilin bind to the vesicle coat and disassemble the clathrin triskelions. Thus, the clathrin coat is rapidly shed after the vesicle pinches off.