Intracellular Protein Trafficking

Question 1

What governs where proteins go ?
Where are these found ?

Answer 1

Signal sequences
Found anywhere in the protein from N, C terminus to middle of the cell

Question 2

What are the 3 types of intracellular trafficking ? Describe them. Include sub types .. Hint ( for TM translocation )

Answer 2

Gated transport - Transport between nuclear pores
Transmembrane translocation - Across membranes
–post-translational
– co-translational.. transported as being synthesized

Vessicular trafficking - mediated by small membrane bound vesicles

Question 3

What are the two forms of GTPase]
Where is Ran GAP and Ran GEF found

Answer 3

The two forms of GTPase is bound to either GTP or GDP
Ran GAP is found in the cytosol and Ran GEF is found in the nucleus, also bound to chromatin

Question 4

Describe the roles of Ran GAP and Ran GEF

Answer 4

Ran GAP - converts GTP into GDP
Ran GEF- converts GDP into GTP

Question 5

Describe how gated transport in and out of the nucleus (Kw: Importins, Exportin , cargo , diffusion

Answer 5

Import of cargo:
Importin can interact with the cargo( containing the nuclear localization signal) and form a complex
This complex can freely diffuse into the nucleus
Ran GTP then interacts with the complex and displaces the cargo protein
The importin-RanGTP complex can then freely diffuse out of the nucleus
RAN GTP is converted to GDP by RAN-GAP and the importin is now free to bind to another cargo protein

Export of cargo
A trimeric complex of Ran-GTP, Cargo protein and exportin is formed in the nucleus
This complex can freely diffuse out of the nucleus
Ran GTP converted to GDP and disrupts the complex … the cargo is released in the cytosol
Exportin can now freely diffuse in the nucleus to transport more protein

Question 6

Describe how gated transport in and out of the nucleus (Kw: Importins, Exportin , cargo , diffusion

Answer 6

Import of cargo:
Importin can interact with the cargo( containing the nuclear localization signal) and form a complex
This complex can freely diffuse into the nucleus
Ran GTP then interacts with the complex and displaces the cargo protein
The importin-RanGTP complex can then freely diffuse out of the nucleus
RAN GTP is converted to GDP by RAN-GAP and the importin is now free to bind to another cargo protein

Export of cargo
A trimeric complex of Ran-GTP, Cargo protein and exportin is formed in the nucleus
This complex can freely diffuse out of the nucleus
Ran GTP converted to GDP and disrupts the complex … the cargo is released in the cytosol
Exportin can now freely diffuse in the nucleus to transport more protein

Question 7

What structures control the diffusion of importin and exportin in and out of the nucleus

Answer 7

Hair like structures ( side of cytosol)
Cage like structures ( side of nucleus)

Question 8

What is required for protein to be transported from the TOM complex to the TIM complex ?

Why is the activity of chaperones important for transmembrane translocation ?

Answer 8

A chemical gradient must occur between the intermembrane space(more positive) and the matrix (more negative )

Chaperones are important for preventing protein aggregation ,and for the correct folding of protein for co-translational translocation