L12 Ubuiquitin Proteasome Proteolic Pathway Flashcards
(21 cards)
What is the ubiquitin proteasome proteolytic pathway (UPPP)?
A selective process for degradation of cellular proteins involving ubiquitin tagging and 26S proteasome action
UPPP is tightly regulated and involves two main steps: ubiquitin conjugation and proteasomal degradation.
What percentage of amino acids released by protein degradation are reutilised?
75%
The remaining amino acids are rapidly degraded.
What is the range of protein half-lives?
30 minutes to 150 hours
What role do lysosomes play in protein degradation?
They degrade extracellular proteins through non-selective proteolysis using hydrolytic enzymes
Lysosomes contain approximately 50 hydrolytic enzymes known as cathepsins.
What is the first step of the ubiquitination process?
Conjugation of multiple ubiquitin moieties to the substrate
What does ubiquitin consist of?
76 amino acid peptide
What are the two types of polyubiquitination sites?
- K48
- K63
What is the function of the E1 enzyme in ubiquitination?
It catalyzes ubiquitin C-terminal acyl-adenylation and forms the ubiquitin-E1 complex
E1 enzymes undergo conformational changes for effective function.
What is the role of E2 enzymes in ubiquitination?
They receive ubiquitin from E1 and transfer it to the substrate protein
There are approximately 40 E2 enzymes in mammals.
What distinguishes E3 ubiquitin ligases?
They transfer activated ubiquitin from E2 to the target protein and control specificity of the ubiquitin system
There are over 600 different E3 ligases in cells.
What are the two subcomplexes of the 26S proteasome?
- 20S core particle (catalytic activity)
- 19S regulatory particle
What is the function of the 19S regulatory particle?
Controls access of ubiquitinated proteins to the 20S proteasome and facilitates unfolding and feeding into the proteolytic chamber
What types of activity are associated with the active sites of the 20S core particle?
- β1: caspase-like activity
- β2: trypsin-like activity
- β5: chymotrypsin-like activity
What are the two pathological states associated with the ubiquitin-proteasome system?
- Loss of function (mutation leading to protein stabilization)
- Gain of function (accelerated degradation of target proteins)
True or False: Proteasome inhibitors have been successful in treating multiple myeloma.
True
What is bortezomib?
A proteasome inhibitor that covalently binds to β5 subunit
It is used in the treatment of multiple myeloma.
What is a limitation of bortezomib?
Little activity against solid tumors and resistance due to β5 mutations
What is carfilzomib?
An irreversible inhibitor of β5 developed from epoxomicin
It is effective in multiple myeloma patients who have previously taken bortezomib.
What are the differences between proteasomes and immunoproteasomes?
- Immunoproteasome expressed in immune cells
- Active site subunits replaced by β5i, β1i, β2i
- Differences may allow selective inhibitors
Fill in the blank: The active site of the immunoproteasome β5i is larger due to distinct conformations of _______.
Met45
What is the significance of PROTACS in drug discovery?
They promote the degradation of problematic proteins by the proteasome
