ER-Golgi Transport

Question 1

Are ATP/GTP required for vesicular transport from ER to Golgi?

Answer 1

No. Sar1 hydrolyses GTP on its own, it is a small GTPase. But when you have nonhydrolyzable GTP the rate jacks way up!!

Question 2

Process of vesicle formation

Answer 2

Sar1-GDP binds the membrane bound Sar1-GEF. GDP exchanged for GTP. You now have active Sar1.
Sar1-GTP binds scaffold proteins Sec23/24, which bind cargo receptors.
Scaffolds also bind COPII.

Question 3

What is the motif that signals Golgi-ER transport?

Answer 3

KDEL

Question 4

Explain process of Golgi/ER transport

Answer 4

Arf1GDP becomes Arf1GTP through a GEF protein. Arf1GTP binds receptors, then attracts COPI proteins. As COPI forms around budding vesicle, it eventually buds off. ArfGAP fits between COPI proteins due to curvature of vesicle, tells ARF1 to hydrolyze its GTP. COPI immediately falls off and you have a free vesicle. COPI is just here to help vesicle form
And leave Golgi.