Vesicle Fusion

Question 1

What is the role of Rab proteins in vesicle fusion?

Answer 1

They recruit recruit tethering proteins on the target membrane. Tethering proteins reach out into the cytosol and the Rabs on the tether interact with a complimentary Rab on the vesicle. This helps pull the vesicle to the membrane so that the SNARE complex can tether.

Of note: Rabs are small GTPases. They are active when bound to GTP. Rab GDP converted to RAB GTP by GEF either at source membrane or in cytosol. RabGTP then stays bound to vesicle and interacts with complimentary RABGTP on target membrane or tethering proteins. This facilitates tethering. There are RABGAPs on the target membrane which hydrolyze the GTP, causing the RABSs to fall apart. Rab then returns to source membrane by diffusion.

Question 2

What role do RAB effectors play?

Answer 2

Rab proteins are specific markers. They recruit and interact with effectors. Effectors bind to motors or act as tethering proteins. They work together to determine target specificity.

Question 3

List 2 roles of Rab in budding/fusion

Answer 3

1. Helps recruit cargo receptors to budding vesicles

2. Helps with vesicle fusion.