Protein Targeting Signals Flashcards
What is the nature of the signal targeting a protein to the ER?
Signal sequence recognised by SRP during translation
Where is the signal to target proteins to the ER located within gut primary sequence?
N-terminus
Are proteins targeted to the ER older or unfolded during transfer?
Unfolded - synthesised through membrane
Which specialist proteins are involved with targeting proteins to the ER?
SRP, SRP receptor, others
Is the signal to target proteins to the ER retained or cleaved
Cleaves by signal peptidase
Does targeting proteins to the ER require energy?
Yes - hydrolysis of GTP by SRP
What is the nature of the signal to target proteins to the nucleus?
NLS = nuclear localising signal
BASIC (Arg/Lys)
May be multipartite
Where is the signal to target proteins to the nucleus located?
Various positions, must be on the surface of the folded protein
Are proteins targeted to the nucleus folded or unfolded during transfer?
Folded - large pores in double membrane of nucleus
Which specialist proteins are involved in the targeting of proteins to the nucleus?
Importing recognises NLS and mediates transport; RanGTP displaces it in nucleus and drives out export cargo
Is the signal to target proteins to the nucleus retained or cleaved?
Retained (facilitates re-importing of proteins when nucleus reforms after cell division)
Does targeting proteins to the nucleus require energy?
Yes - hydrolysis of GTP
Describe the nature of the signal to target proteins to the mitochondria
Amphipathic signal for initial targeting to Matrix - may be extra signals to other final destinations
Where is the signal to target proteins to the mitochondria located within the primary sequence?
N terminus (or internal stop transfer = hydrophobic)
Are proteins targeted to the mitochondria folded or unfolded during transfer?
Held partially unfolded by chaperones e.g. MSF
