11. Protein Targeting Flashcards
What signal is used to return escaped resident ER proteins?
KDEL sequence
Where is the KDEL sequence?
C-terminal
How does the KDEL sequence redirect the protein back to the ER?
KDEL receptor in the golgi binds to it and it returns in a COP1 coated vesicle back to the ER.
What causes release of the protein when it is back in the ER?
The ER has a higher pH then the golgi (pH7 in ER and 6.5 in golgi), causing the receptor to release the protein.
What is the role of a COP2 transporter?
It transports vesicles from ER to Golgi.
What is the signal sequence for targeting to lysosomes?
Mannose-6-phosphate
Where is M6P signal added onto lysosomal proteins?
In the Cis face of the Golgi apparatus
How does the M6P signal direct the protein to the lysosome?
It binds to the M6P receptor in a clathrin-coated vesicle at the trans face of the Golgi and travels to the lysosome where the acidic environment causes release of the protein.
Is the protein folded or unfolded during lysosome targeting?
Folded
What is the signal sequence to target proteins to the mitochondria?
Amphipathic N-terminal signal (MTS - matrix targeting sequence)
Is the protein folded or unfolded during mitochondrial transport? Explain how this is sustained.
unfolded, kept unfolded by chaperones - Hsc 70
What does the MTS bind to in order to enter the mitochondria?
It binds to import receptor enters through a pore called TOM on the outer membrane. It then moves through a TIM channel on the inner membrane and the targeting signal is cleaved.
Where is the mitochondrial targeting sequence?
N-terminal
What involves ATP energy in the process of mitochondrial targeting?
HSC70 chaperone binding to the protein to keep it unfolded requires ATP energy
What signal is used to target proteins to the nucleus?
Nuclear localisation sequence (NLS)
