Flashcards in MCBG - Protein Targeting Table Deck (16):
Which types of proteins do we need to know about?
Targeted to ER, nucleus, mitochondria, lysosomes, retention in ER
Which proteins have their signal found on the N-terminus?
To ER, to mitochondria
Which proteins have their signal on the C-terminus?
Retention in ER
Which proteins have their signal sequence in various positions on the surface of the folded protein?
Which proteins have a signal patch to distinguish from other mannose-labelled proteins?
Which proteins are folded during transfer?
To nucleus, to lysosomes and retention in ER.
Which proteins are unfolded during transfer?
Which proteins are held partially unfolded by chaperone proteins?
What happens to the signals once the various proteins reach their target destination?
- Cleaved (ER, mitochondria)
- Retained (nucleus, retention in ER)
- phosphate removed by phosphatase (lysosomes)
Which types of protein targeting require energy?
- To ER (hydrolysis of GTP)
- To nucleus (hydrolysis of GTP)
- To mitochondria (ATP hydrolysis)
- To lysosomes (indirect use of ATP)
Which protein targeting does not use energy?
Retention in ER (binding and release is dependent on pH)
What is the nature of the signal to the ER, and what specialist proteins are involved?
- signal sequence recognised by SRP during translation
- signal recognition protein (SRP), SRP receptor
What is the nature of the signal to the nucleus, and what specialist proteins are involved?
- nuclear localising signal (basic)
- importin recognises NLS and mediates transport, RanGTP displaces it in nucleus
What is the nature of the signal to the mitochondria, and what specialist proteins are involved?
- amphipathic signal for targeting to matrix
- mitochondrial-import stimulating factor, "Tom and Tim" channel complex
What is the nature of the signal to the lysosomes, and what specialist proteins are involved?
- post-translation addition of mannose-6-phosphate
- M-6-P receptors in trans-Golgi