L19: Proteolysis 2 (Latency and Activation)

Question 1

What is the primary function of proteases in biological reactions?

Answer 1

Proteases cleave proteins, which can either inactivate them or activate them by processing latent forms into biologically active forms.

Question 2

Why is proteolytic activation considered a rapid response mechanism?

Answer 2

It is faster to activate a latent protein via proteolysis than to synthesize a new protein through transcription and translation.

Question 3

Name three families of proteases involved in latency and activation discussed in the lecture.

Answer 3

1. Proprotein convertases (PCSKs)
2. Matrix metalloproteases (MMPs)
3. Secretases

Question 4

What is the role of propeptides in protein activation?

Answer 4

Propeptides need to be cleaved for activation, aiding in proper folding and ensuring proteins are activated only when necessary.

Question 5

What is the difference between constitutive and regulated secretory pathways?

Answer 5

• Constitutive pathway: Directly delivers cargo to the plasma membrane.
• Regulated pathway: Stores cargo in vesicles and releases it in response to specific signals.

Question 6

How do PCSKs contribute to hormone maturation?

Answer 6

PCSKs cleave prohormones like proinsulin into their active forms, enabling their biological function.

Question 7

What role does PCSK9 play in cholesterol metabolism?

Answer 7

PCSK9 promotes LDL receptor degradation in lysosomes, reducing the number of receptors on the plasma membrane and decreasing LDL clearance from circulation.

Question 8

How do viruses exploit PCSKs for cell entry?

Answer 8

Viruses like SARS-CoV-2 use PCSKs such as furin to cleave glycoproteins, altering protein conformation and facilitating viral entry into host cells.

Question 9

What is the significance of the furin cleavage site in the SARS-CoV-2 spike protein?

Answer 9

The furin cleavage site enhances viral entry by enabling better binding to the ACE2 receptor, contributing to higher virulence compared to SARS-CoV-1.

Question 10

What is the ‘cysteine switch mechanism’ in matrix metalloproteases (MMPs)?

Answer 10

The propeptides of MMPs coordinates with a zinc ion to keep the enzyme inactive until cleavage removes the propeptides, activating the enzyme.

Question 11

Name a key role of matrix metalloproteases (MMPs) in cancer progression.

Answer 11

MMPs facilitate tumour growth and metastasis by degrading the extracellular matrix, promoting angiogenesis, and enabling tumour invasion.

Question 12

What is the role of secretases in Alzheimer’s disease?

Answer 12

Beta and gamma secretases cleave amyloid precursor protein, forming amyloid-beta peptides, which aggregate into plaques associated with Alzheimer’s pathology.

Question 13

How can PCSK9 inhibitors be used therapeutically?

Answer 13

PCSK9 inhibitors increase LDL receptor recycling to the plasma membrane, improving cholesterol clearance and treating hypercholesterolemia.

Question 14

What are amyloid plaques and their relevance in Alzheimer’s?

Answer 14

Amyloid plaques are aggregates of amyloid-beta peptides, formed due to beta and gamma secretase activity, and are toxic to neurons.

Question 15

What are proprotein convertases (PCSKs), and what is their primary function?

Answer 15

PCSKs are serine proteases involved in protein maturation, receptor recycling, and are exploited by pathogens for activation processes.

Question 16

What are the typical cleavage site characteristics of PCSKs?

Answer 16

PCSKs cleave at sites containing 2-5 basic residues, primarily arginine and lysine, regulated by pH and calcium levels.

Question 17

How does the cleavage of proproteins by PCSKs benefit viruses like HIV-1?

Answer 17

PCSKs cleave viral glycoproteins, such as glycoprotein 160 in HIV-1, enabling their activation and enhancing viral infectivity.

Question 18

Describe the functional domains commonly found in PCSKs.

Answer 18

PCSKs typically have a signal peptide, a propeptides for auto-catalytic activation, a catalytic domain, and a P domain regulated by calcium.

Question 19

How do matrix metalloproteases (MMPs) contribute to tissue remodelling?

Answer 19

MMPs degrade components of the extracellular matrix, facilitating processes like wound healing, morphogenesis, and inflammation.

Question 20

What is the role of MMP-2 and MMP-9 in late-stage prostate cancer?

Answer 20

These MMPs activate pathways leading to extracellular matrix degradation and the production of soluble RANKL, which promotes bone degradation.

Question 21

How are MMPs activated from their latent forms?

Answer 21

The propeptides of MMPs is removed, disengaging the zinc ion from the catalytic site, which activates the enzyme—a process called the cysteine switch.

Question 22

Why are MMP inhibitors important in clinical research?

Answer 22

MMP inhibitors target the catalytic zinc site, aiming to block extracellular matrix degradation in diseases like cancer and inflammatory disorders.

Question 23

What is a key pathological role of gamma secretases in Alzheimer’s disease?

Answer 23

Gamma secretases generate amyloid-beta peptides, contributing to plaque formation in neuronal tissues, which are toxic to neurons.

Question 24

What is the function of the ADAM family of proteins?

Answer 24

ADAM proteins are metalloproteases involved in cleaving membrane-anchored proteins, regulating pathways such as TNF-alpha and growth factor signalling.

Question 25

What therapeutic strategies target secretases in Alzheimer’s disease?

Answer 25

Inhibitors of beta and gamma secretases are developed to reduce amyloid-beta plaque formation and mitigate neurotoxicity.

Question 26

How does SARS-CoV-2 exploit furin (PCSK3) for cell entry?

Answer 26

Furin cleaves the spike protein of SARS-CoV-2, enabling conformational changes that enhance binding to ACE2 receptors and viral entry into cells.

Question 27

Compare SARS-CoV-1 and SARS-CoV-2 in terms of furin cleavage sites.

Answer 27

SARS-CoV-2 has a furin cleavage site that enhances its virulence, while SARS-CoV-1 lacks this site, resulting in lower efficiency of cell entry.

Question 28

Why is the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein significant?

Answer 28

The RBD interacts with ACE2 receptors, and furin cleavage facilitates its ‘standing up’ conformation for efficient receptor binding.

Question 29

What is a secretagogue?

Answer 29

A secretagogue is a substance that triggers the secretion of another substance, often playing a role in regulated pathways of vesicular exocytosis.

Question 30

How do secretases contribute to protein shedding?

Answer 30

Secretases cleave membrane-bound proteins, releasing their extracellular domains to regulate processes like growth factor activation and receptor signalling.

Question 31

What are intramolecular chaperones, and what is their role in proteolytic activation?

Answer 31

Intramolecular chaperones are parts of propeptides that assist in the correct folding of proteins during latency, ensuring proper conformation for activation.

Question 32

Describe the process of protein sorting through the Golgi apparatus.

Answer 32

Proteins are synthesized in the endoplasmic reticulum, modified (e.g., glycosylation) in the Golgi, and sorted into either constitutive pathway for direct secretion or regulated pathways for signal-dependent exocytosis.

Question 33

What is the role of pre-peptides in protein synthesis?

Answer 33

Pre-peptides, also known as signal peptides, guide newly synthesized proteins into the endoplasmic reticulum and are cleaved off during protein maturation.

Question 34

How do PCSKs recognize and cleave their substrates?

Answer 34

PCSKs recognize specific sequences around cleavage sites, typically with 2-5 basic residues like arginine and lysine, to cleave propeptides and activate proteins.

Question 35

What is the significance of tissue-specific expression of PCSKs?

Answer 35

Tissue-specific PCSK expression allows tailored activation of proproteins, such as hormones or enzymes, to meet the distinct functional needs of different tissues.

Question 36

Explain the role of PCSK1 and PCSK2 in hormone maturation.

Answer 36

PCSK1 and PCSK2 process prohormones like proinsulin into active forms, ensuring proper folding and functionality of hormones within regulated secretory pathways.

Question 37

Why is the production of polyproteins advantageous for cells?

Answer 37

Polyproteins allow the efficient synthesis of multiple proteins from a single gene, saving energy and enabling coordinated regulation of protein production.

Question 38

What roles do MMPs play in wound healing?

Answer 38

MMPs degrade and remodel the extracellular matrix, clearing damaged tissue and promoting cell migration and angiogenesis necessary for wound repair.

Question 39

How does MMP dysregulation contribute to cancer progression?

Answer 39

Dysregulated MMPs enhance tumour invasion, metastasis, and angiogenesis by breaking down the extracellular matrix and modifying the tumour microenvironment.

Question 40

What is the function of ADAM17 in cellular signalling?

Answer 40

ADAM17 cleaves membrane-bound proteins like TNF-alpha precursors, releasing their active forms and regulating inflammatory and immune responses.

Question 41

How do beta and gamma secretases differ in processing amyloid precursor protein (APP)?

Answer 41

• Beta secretase: Initiates amyloidogenic cleavage of APP.
• Gamma secretase: Cleaves APP further to produce amyloid-beta peptides, contributing to plaque formation in Alzheimer’s disease.

Question 42

How does the SARS-CoV-2 spike protein remain infectious after furin cleavage?

Answer 42

The cleaved portions of the spike protein remain non-covalently bound, altering the conformation to facilitate binding to ACE2 receptors and enhancing infectivity.

Question 43

What is the cysteine switch mechanism in MMPs?

Answer 43

The cysteine in the propeptides domain coordinates with the zinc ion, keeping MMPs inactive until cleavage disrupts this interaction, activating the enzyme.

Question 44

What makes secretases a therapeutic target in Alzheimer’s disease?

Answer 44

Inhibiting beta and gamma secretases can reduce amyloid-beta production, potentially slowing plaque formation and neurotoxicity in Alzheimer’s patients.

Question 45

Why are MMP inhibitors challenging to develop as drugs?

Answer 45

MMP inhibitors often fail in clinical trials due to off-target effects and difficulty achieving selective inhibition of specific MMPs without affecting others.

Question 46

What distinguishes regulated from constitutive secretory pathways?

Answer 46

Regulated pathways store vesicles until specific signals trigger secretion, while constitutive pathways continuously deliver contents to the plasma membrane.

Question 47

Describe the process of LDL receptor recycling and PCSK9’s involvement.

Answer 47

LDL receptors are normally recycled to the plasma membrane after LDL dissociation, but PCSK9 directs them to lysosomes for degradation, reducing LDL clearance.

Question 48

How does furin cleavage enhance SARS-CoV-2 virulence compared to SARS-CoV-1?

Answer 48

SARS-CoV-2’s furin cleavage site enables better spike protein activation and ACE2 receptor binding, increasing its ability to infect human cells.

Question 49

What is the role of soluble RANKL in late-stage prostate cancer?

Answer 49

Soluble RANKL, produced by MMP7 cleavage, promotes bone degradation, contributing to the osteolytic effects seen in advanced prostate cancer.

Question 50

Why is early-onset Alzheimer’s linked to mutations in presenilin proteins?

Answer 50

Mutations in presenilin proteins, components of gamma secretase, increase catalytic activity, leading to overproduction of amyloid-beta peptides and early plaque formation.