3. ARF1 GTPase is a coat-recruitment protein, in the Golgi, similar to SAR1 GTPa
ID: 255972 • Letter: 3
Question
3. ARF1 GTPase is a coat-recruitment protein, in the Golgi, similar to SAR1 GTPase in the ER. A. (1pt) What type of coat protein does ARF1 GTPase most likely assemble? B. (3pts) Imagine that the ARF1 GTPase protein was mutated so that it could not hydrolyze GTP into GDP, regardless of its binding partners. Would you expect ARF1-initiated transport vesicles to bud off normally? How might subsequent or downstream steps in transport be affected if ARF1 cannot hydrolyze GTP into GDP? C. (3pts) What if the ARF1 protein was mutated so that it was locked in a GDP-bound state, transport vesicle coat formation? D. (2pts) Please identify two plausible cellular destinations of vesicles associated with ARF1 GTPase. Additionally, please predict which type of motor protein is most likely involved in vesicle transport to these destinations.Explanation / Answer
Answer 3.A) Arf1 are known to recruit coatomer coat proteins (COP-I and COP-II).
Answer 3.B) The GTPase activity is required to shed coat proteins from coated vesicles. Mutation in Arf1 leading to unable to hydrolyze the bound GTP will not prevent the budding of coated vesicles. But it will prevent the shedding thus trapping the cargo in coated vesicles inhibiting further processes.
Answer 3.C) Since GTP exchange is required from Arf-GDP bound state to form active Arf-GTP which recruits coat protein and initiate vesicle formation and budding, locking of Arf in GDP bound state will prevent recruitment of coat protein and vesicle formation.
Answer 3.D) The two possible destinations include cell membrane where vesicle with cargo destined to cell surface are pinched off to fuse with cell membrane. Second destination include endosome which is widely used by pathogens to gain entry (retrograde transport). The microtubule based motor kinesins proteins are most commonly involved in anterograde vesicular transport while dynein motor proteins are involved in reterograde vesicular transport (endosome).
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