Lecture 8 - Ubiquitin Signalling 2

Question 1

DUB catalytic triad (of thiol-proteases) is formed by which 3 amino acids?

Answer 1

DUB catalytic triad (of thiol-proteases) is formed by Asp, His, and Cys

Question 2

Catalytic triad of DUBs enables what?

Answer 2

Enables cleavage of bonds between Ubiquitins

Question 3

MetalloDUBs active site is formed by which amino acids?

Answer 3

Glu, His, His, Asp, and Ser

His, His, and Asp coordinate a Zn2+ atom

Question 4

Factors to consider for substrate selectivity:

Answer 4

1. Ubiquitin vs Ubiquitin-Like modifier cleavage
2. Ub chain vs substrate recognition
3. Exo- vs Endo-Cleavage
4. Specialised Cleavage Modes

Question 5

DUBs can be regulated by oxidation

TRUE OR FALSE

Answer 5

TRUE

S- of Cys -> SOH (Sulphonic Acid), this is a reversible process, so return to a reducing environment will reactivate the DUBs activity

NB: This is not the only way they are regulated

Question 6

Steps involved in degradation in the proteasome:

Answer 6

• Initiation (ubiquitination of substrate)
• Engagement
• Deubiquitination (Ubiquitin is thermostable, so needs to be removed or will clog the proteome)
• Degradation

Question 7

Proteasomal DUBs role is in recycling ubiquitin

TRUE OR FALSE

Answer 7

TRUE

Question 8

DUBs on the proteasome:

Answer 8

Uch37
Usp14
Rpn11 (Cleaves last Ubiquitin of the substrate, deeper in the proteasome than Uch37 and Usp14)

Question 9

Residence time at the proteome will determine whether a protein is degraded or not
TRUE OR FALSE

Answer 9

TRUE