Cell Biology - proteolysis

Question 1

What is proteolysis?

Answer 1

The breakdown of proteins into smaller polypeptides or amino acids

Question 2

Where does proteolysis occur?

Answer 2

proteasomes or lysosomes

Question 3

What is ubiquitin?

Answer 3

A small regulatory protein used to mark protein degradation

Question 4

What are the 3 main steps of ubiquitylation?

Answer 4

• activation using ubiquitin activating enzymes (E1s)
• conjugation using ubiquiting-conjugating enzymes (E2s)
• Ligation using ubiquitin ligases (E3s)

polyubiquitylated proteins are recognised by the 26S proteasome and degraded

Question 5

What is the purpose of monoubiquitylation?

Answer 5

regulates protein interactions within cells

Question 6

What is APC/C?

Answer 6

• anaphase promoting complex/cyclosome
• an E3 ubiquitin ligase
• regulates progression through mitosis and G1

Question 7

How does APC/C become activated and what does it do?

Answer 7

• becomes activated when spindle binds to chromosomes
• this activates separase
• this cleaves cohesin
• allows chromosomes to split and move to opposite ends of the cell

Question 8

What are some examples of E2 enzymes and what do the do?

Answer 8

• UbE2C initiates ubiquitin chain formation
• UbE2S elongates ubiquitin chains
• UbcH10 is a proto-oncogene

Question 9

How is ubiquitin activated and attached onto the protein to be degraded?

Answer 9

Ubiquitin is activated by the hydrolysis of ATP. The glycine at the end of the ubiquitin forms an isopeptide bind to a lysine on the protein.

Question 10

What are the two subunits of the proteasome and how many are there of each unit?

Answer 10

20S x1

19S x2

Question 11

What is the structure of the 20S subunit?

Answer 11

2 types of subunit - alpha and beta
4 rings:
2 outer rings are 7 alpha subunits
2 inner rings are 7 beta subunits 
The hollow space in the middle is known as the barrel core and is where protein degradation occurs

Question 12

What is the purpose of the 19S subunit?

Answer 12

locate and bind polyubiquitinated proteins for degradation

ATPase activity allows 19S subunit to start unfolding protein so it can fit in 20S core`

Question 13

What is the fate of ubiquitin?

Answer 13

Cleaved by isopeptidases and recycled

Question 14

What are some classes of proteasome inhibitors?

Answer 14

peptide aldehydes
boronates
epoxyketone
beta-lactone

Question 15

What is the immunoproteasome for?

Answer 15

antigen presentation

Question 16

What does K63 do?

Answer 16

targets proteins to be degraded by lysosomes

Question 17

What are the two proteins commonly mutated in Parkinson’s

Answer 17

PINK1 phosphorylates parkin and ubiquitin

Parkin which is an E3 ubiquitin ligase

Question 18

What are pro-peptides for?

Answer 18

• allows correct folding of protein
• assembly of multimers
• must be removed for activity

Question 19

What are PCSKs?

Answer 19

• propeptin convertases subtilisin.kexin

- activate other proteins by propeptide cleavage