Question

What controls the ability of a vesicle to fuse with its appropriate target organelle? Be sure to describe how this process mediates fusion.

Answer 1

Vesicles play important role in transport of materials between different membrane enclosed compartments in the cell.

This transport is specific and based on selective packaging of cargo into the vesicles which will recognize and fuse only with the target membrane.

The vesicles are coated with proteins by budding from a membrane.

There are 3 types of coat proteins. Clathrin coated proteins ( bud from plasma membrane as well as trans golgi to lysosomes), COP II coated proteins (bud from ER to cis Golgi) and Cop I coated proteins (bud from ER-Golgi intermediate and function in retrieval of resident proteins to ER and Golgi).

Assembly of coat proteins requires GTP binding proteins called ARF and Sar 1.

Fusion of transport vesicle to target membrane involves specific recognition of target membrane and fusion to deliver its content to target organelle.

Vesicle fusion is mediated by specific proteins called SNAREs. v-SNAREs on vesicle membrane and t-SNAREs on target membranes are present. Complex formation between v-SNAREs and t-SNAREs leads to membrane fusion. Other protein such as Rab which is a GTP binding protein is also require to regulate and facilitate the SNAREs complex. Following the membrane fusion NSF/SNAP proteins disassemble SNAREs complex.