the ubiquitin system

Question 1

Describe the main protein turnover pathways.

Answer 1

The main protein turnover pathways include the endosome-lysosome pathway, the ubiquitin-proteasome pathway, and the mitochondrial proteolytic system.

Question 2

Define protein turnover regulation and explain its importance.

Answer 2

Protein turnover regulation refers to the control and maintenance of protein levels in cells. It is crucial for metabolic flexibility, quality control, T-cell activation, and removal of abnormal proteins.

Question 3

How is protein turnover regulated in cells?

Answer 3

Protein turnover is regulated through processes like ubiquitination, proteasomal degradation, and autophagy, ensuring proper protein homeostasis.

Question 4

What are the therapeutic applications of understanding protein turnover?

Answer 4

Understanding protein turnover can lead to the development of therapies for conditions related to protein misfolding, abnormal degradation, and metabolic disorders.

Question 5

Describe the process of polyubiquitination.

Answer 5

Polyubiquitination involves target proteins being ubiquitinated at multiple lysine residues, with ubiquitin itself being ubiquitinated up to 10 times, often at Lysine-48 for secondary ubiquitination.

Question 6

Explain the molecular basis of protein turnover involving ubiquitination.

Answer 6

Ubiquitination involves the covalent attachment of ubiquitin to intracellular proteins, marking them for degradation. It is a highly conserved post-translational modification essential for protein degradation.

Question 7

What is the significance of the C-terminal Gly-Gly dipeptide in ubiquitin?

Answer 7

The C-terminal Gly-Gly dipeptide in ubiquitin is crucial for attaching ubiquitin to target proteins via the e-amino group of lysine, forming a peptide bond.

Question 8

How do the two types of polyubiquitylation differ in the linkage of ubiquitin molecules?

Answer 8

The two types of polyubiquitylation differ in how the ubiquitin molecules are linked together, with Lysine-48 being the site of secondary ubiquitination in one type.

Question 9

Define the Ubiquitin Proteasome System (UPS) and its role in protein degradation.

Answer 9

The UPS is a proteolytic system that degrades proteins from the cytoplasm, nucleus, and ER. It plays a crucial role in maintaining protein homeostasis and removing abnormal or misfolded proteins.

Question 10

Explain the cooperation between lysosomes and endosomes in protein degradation.

Answer 10

Lysosomes and endosomes cooperate in degrading extracellular and cell-surface proteins through the endosome-lysosome pathway, contributing to cellular homeostasis and waste management.

Question 11

Describe the significance of linkage through Lys48 in protein degradation

Answer 11

Lys48 linkage signifies degradation by the proteasome.

Question 12

What is the process of ubiquitination?

Answer 12

Ubiquitination is a multistep enzyme-dependent pathway.

Question 13

Define the Ubiquitin cascade

Answer 13

The Ubiquitin cascade is a pyramid structure.

Question 14

How does the proteasome deal with Lys48 Poly-Ub substrates?

Answer 14

The 20S Proteasome deals with Lys48 Poly-Ub substrates.

Question 15

What is the role of the E1 enzyme in the ubiquitin-dependent proteolysis pathway?

Answer 15

E1 activates ubiquitin.

Question 16

Describe the structure of the proteasome

Answer 16

The proteasome is a huge protein complex with a 20S central cylinder.

Question 17

What are the different catalytic activities of the proteases found within the proteasome?

Answer 17

The proteases have chymotrypsin-like, trypsin-like, and caspase-like activities.

Question 18

How does the proteasome perform processive protein digestion?

Answer 18

The proteasome cap contains ATPases that unfold the protein substrate.

Question 19

Explain the impact of glycosylation on the proteasome under different nutritional conditions

Answer 19

High glucose leads to decreased intracellular proteolysis through glycosylation, while low nutrition increases proteolysis.

Question 20

What is the potential role of the proteasome as a nutrition sensor?

Answer 20

The proteasome’s glycosylation responsiveness to nutrition suggests it may act as a nutrition sensor.

Question 21

Describe the role of Velcade (bortezomib) in inhibiting proteasome activity.

Answer 21

Velcade is a small molecule inhibitor of proteasome proteolytic activity, specifically inhibiting chymotrypsin-like activity.

Question 22

Define the Ubiquitin-Proteasome system.

Answer 22

The Ubiquitin-Proteasome system involves tagging proteins with ubiquitin for degradation in the proteasome.

Question 23

How does the Ubiqu system contribute to defining the normal biological function of proteins?

Answer 23

Understanding the Ubiquitin system is important for defining the normal biological function of proteins and is linked to many disease mechanisms.

Question 24

What is the significance of E3 ligase inhibition in research and potential therapies?

Answer 24

E3 ligase inhibition promises a high degree of specificity and is an area of intense research interest.

Question 25

Do proteasome inhibitors sensitize cells to apoptosis?

Answer 25

Yes, proteasome inhibitors like Velcade sensitize cells to apoptosis, although the mechanism is not well understood.

Question 26

Describe the different types of Ubiquitination and their biological outcomes.

Answer 26

There are different types of Ubiquitination such as Poly-Ub and Mono-Ub, each with different biological outcomes.

Question 27

How do HECT E3s differ from RING finger E3s in terms of structure and function?

Answer 27

HECT E3s are single subunit E3 ligases with a HECT domain, while RING finger E3s can be single subunit or multisubunit with a RING domain.

Question 28

Define the role of E2 enzymes in the Ubiquitin system.

Answer 28

E2 enzymes provide catalytic activity in the Ubiquitin system, working in conjunction with E3 ligases to transfer ubiquitin to target proteins.

Question 29

What is the function of APC (Anaphase promoting complex) in the Ubiquitin system?

Answer 29

APC is a multisubunit E3 RING ligase that regulates Cyclin levels during the Cell Cycle.

Question 30

Describe the characteristics of NEDD4 subfamily E3 Ubiquitin Ligases.

Answer 30

NEDD4 subfamily E3 Ubiquitin Ligases are characterized by the presence of a WW domain and a C2 domain that can bind to membranes in response to changes in intracellular Ca2+ levels.

Question 31

Describe the role of ENaC in the kidney.

Answer 31

ENaC is a major ion channel responsible for controlling salt and fluid reabsorption in the kidney.

Question 32

What is Liddle’s syndrome and how is it caused?

Answer 32

Liddle’s syndrome is an inherited form of hypertension caused by mutations in the PPXY motif, leading to accumulation of ENaC channels at the cell surface.

Question 33

Define Deubiquitinating enzymes (DUBs) and their role in the Ubiquitin-Proteasome system.

Answer 33

DUBs are enzymes that remove ubiquitin molecules from proteins, playing a crucial role in regulating protein stability and turnover in the Ubiquitin-Proteasome system.

Question 34

How does impairment of Nedd4-2 contribute to Liddle syndrome?

Answer 34

In Liddle syndrome, deletion or mutation of the PY motif in ENaC impairs Nedd4-2’s ability to bind and ubiquitinate ENaC, leading to its accumulation at the plasma membrane and increased channel activity.

Question 35

Describe the regulation of ENaC surface stability.

Answer 35

ENaC surface stability is regulated by Deubiquitinating enzymes (DUBs) which help maintain the appropriate levels of ENaC channels on the cell membrane.

Question 36

What are the sites of action for diuretic therapy involving ENaC?

Answer 36

Diuretic therapy targeting ENaC includes the use of Carbonic anhydrase inhibitors like Acetazolamide to affect ion channels in the collecting duct.

Question 37

How is sodium balance maintained in the kidney involving ENaC?

Answer 37

Sodium balance in the kidney is maintained by the Na+/K+ ATPase generating a concentration gradient to facilitate sodium movement through ENaC in the collecting duct epithelium.

Question 38

Define the primary role of ENaC channels in the renal collecting duct.

Answer 38

The primary role of ENaC channels is the reabsorption of sodium in the renal collecting duct to regulate salt and fluid balance.

Question 39

What is the treatment approach for Liddle syndrome?

Answer 39

The treatment for Liddle syndrome involves a low-sodium diet and the use of potassium-sparing diuretics that directly block the sodium channel.

Question 40

Describe the impact of mutations in the substrate for E3 ligase on Liddle’s disease.

Answer 40

Mutations in the substrate for E3 ligase can cause Liddle’s disease by affecting the turnover of ENaC channels, leading to abnormal salt and fluid resorption.

Question 41

Describe the purpose of potassium-sparing diuretics like amiloride triamterene.

Answer 41

To treat hypertension and hypokalemia without needing additional potassium replacement therapy.

Question 42

What is the medical treatment outcome for patients with Liddle Disease?

Answer 42

Correction of hypertension and hypokalemia.

Question 43

How does mutation of ubiquitination sites in ENAC relate to Liddle’s Disease?

Answer 43

It causes the accumulation of ENAC, similar to the artificial mutation seen in Liddle’s Disease.

Question 44

Define protein degradation diseases and provide examples like cancer and Angelman’s syndrome.

Answer 44

Diseases where protein degradation is affected, such as cancer (VHL mutations) and Angelman’s syndrome (E6-AP mutation).

Question 45

What is the common cause for kidney cancers and what is its role in ubiquitin ligase?

Answer 45

VHL mutations; it is a component of a ubiquitin ligase.

Question 46

Describe the impact of disruption of the Itch gene in mice.

Answer 46

It causes syndromes affecting the immune system, skin inflammation, severe itching, and scarring.

Question 47

What is the role of Nedd4 in Liddle syndrome?

Answer 47

Nedd4 is a ubiquitin protein ligase that binds ENaC subunits, and mutation in ENaC leads to altered homeostasis and hypertension.