Ubiquitylation Flashcards
What is ubiquitin and what is it’s size?
A small conserved heat stable protein, it is 76 amino acids
What is ubiquitin’s characteristics? Where is it found?
It can survive extreme heats and pH and proteolysis. It’s found in eukaryotes and archae but not eubacteria and in all cell types
How does ubiquitylation works?
It covalently modifies proteins in an ATP dependent manner, it attaches UB to the lysine residue of the target protein
What are the ubiqiuitin genes in humans?
UBA,UBB, UBC expressed as fusion proteins
What parts of the protein is conserved?
N terminal and lysine residues in certain positions such as 48
What are E1 and E2 and what are there functions? What part of them is conserved?
E1 (has two genes in humans) and E2(coded by family of genes) are enzymes that require ATP. E2 can be used for DNA repair and can be regulatory proteins. But both ubiquitinates. They have conserved cys residue
What’s E3? What are the main families? What is it’s function?
It’s ubiquitin ligase enzyme coded by many genes.
Has two major families:
1. HECT E3
2. RING- conserved cys residue, functions in insolation and in multi protein complex, has a modified zinc finger.
It’s function is to recognize substrate
Outline the ubiquitylation process.
First the ub binds to E1 after ATP hydrolysis and then it passes it to E2 and then E3 will bind to it and recognize the target substrate and deposit the UB and it’ll be degraded through the K48 lysine residue in proteosome 26. The UB can be recycled, if there are more 4 ub it’ll be degraded, it can also de-ubiquitinated if less than 4 ub.
What does k63 lysine residue do found in the ub?
It is involved in the DNA repair.
What targets get ubiquitylated?
PEST element-rich in pro,glu,ser,thr AA
pHOSPHORYLATION
D-BOX- found in mitotic cyclins targeted by anaphase promoting complex
and MATA2 and N end rule
What’s the proteosome?
A huge complex 26S that made up of 2 sub-complexes; 19 S and 20S
It is atp DEPENDENT.
What’s the difference between the two sub complexes found in 26 proteosome?
a20S is core subuint and 19 S is regulatory subunit cap. The proteins that are ubiquitinated they pass through the regulatory sub complex first and they are recognized and removed and unfolded using ATP hydrolysis and then it passes through the core and cleaved and then let out.
Overview of the 26 proteasome
It’s a threonine protease and has 19S cap that has non redundant ATPases; chaperone activity.
Can act as an inhibitor
What is DUB? How does it work?
It’s deubiquitylating enzyme that has thiol protease and a conserved cys residue. It removes conjugates or fusions of UB, the region next to the c-terminal GG needs to be present for it work.
Outline the biological functions of ubiquitin proteosome system
Used in transcription, immune response, cell cycle, metabolism, signal transduction and DNA repair, regulates all of these processes
