Session 9: Post-translational Modification and Protein Targeting Flashcards
What is post-translational modification?
The processing that some proteins undergo following their production via translation
Where are some common subcellular locations of protein targeting for sorting?
Endoplasmic reticulum
Lysosomes
Mitochondria
Nucleus
What 4 things are required for protein sorting?
A signal
A receptor that recognises the signal and directs to the correct membrane
Translocation machinery
Energy to transfer the protein to its new place
What is the nature of signal targeting proteins to the ER?
A signal sequence that is recognised by SRP during translation
What is the location of the signal within the primary sequence of proteins destined for the ER?
N- terminus
Is the protein folded or unfolded during transfer to the ER?
Unfolded
What specialist proteins are involved in targeting proteins to the ER?
Signal Recognition Protein (SRP)
SRP receptor
Is the signal retained or cleaved once it reaches the ER?
Cleaved by signal peptidase
Does the process of targeting proteins to the ER require energy?
Yes. the hydrolysis of GTP by SRP
What is the nature of the targeting signal needed to direct proteins to the nucleus?
Nuclear Localising Signal (NLS) Basic sequence (Arg/Lys)
Where is the primary sequence of the targeting signal located on proteins destined for the nucleus?
On the surface of folded protein
Are the proteins that are destined for the nucleus folded or unfolded during transfer?
Folded
They pass through large pores in the nuclear membrane
What specialist proteins are involved in the trafficking of proteins to the nucleus?
Carrier protein: Importin
RanGTP
Is the signal retained or cleaved once it reaches the nucleus?
Retained
Does the process of targeting signals to the nucleus require energy?
Yes, the hydrolysis of GTP
What is the nature of the targeting signal that sends proteins to mitochondria?
It is an amphipathic signal that targets proteins to the matrix
What is the location of the signal within the primary sequence of proteins destined for mitochondria?
N-terminus
Are the proteins that are destined for mitochondria folded or unfolded during transfer?
They are held partially folded by chaperones
What specialist proteins are involved in the trafficking of proteins to the mitochondria?
MSF
Tom and Tim
Is the signal retained or cleaved once the protein has been delivered to mitochondria?
The signal is cleaved
Does the process of targeting signals to mitochondria require energy?
Yes, requires ATP
What is the nature of the targeting signal needed to direct proteins to lysosomes?
Post translational addition of Mannose-6-Phosphate
Phosphate is added to 6th carbon on mannose sugar in the golgi
Where is the primary sequence of the targeting signal located on proteins destined for lysosomes?
Must be signal patch to distinguish lysosomal proteins from other mannose-labelled proteins
Are the proteins that are destined for the nucleus folded or unfolded during transfer to lysosomes?
Folded (delivered via vesicle)
What specialist proteins are involved in the trafficking of proteins to the lysosomes?
M6P receptor in the trans-golgi
Is the signal retained or cleaved once the protein has been delivered to lysosomes?
Phosphate is removed by phosphatase
Does the process of targeting signals to lysosomes require energy?
The process requires INDIRECT use of ATP to remove the phosphate
What is the nature of the targeting signal needed to retain proteins in the ER?
KDEL
Where is the primary sequence of the targeting signal located on proteins destined to be retained in the ER?
C-terminus
Are the proteins that are destined for the nucleus folded or unfolded during ER retention?
Folded (delivered via vesicle)
What specialist proteins are involved in the trafficking of proteins to be retained in the ER?
KDEL and KDEL receptor in cis-golgi
Is the signal retained or cleaved once the protein is retained in the ER?
Retained
Does the process of retaining proteins in the ER require energy?
No, no energy is required
