L19: Proteolysis 2 (Latency and Activation) Flashcards
What is the primary function of proteases in biological reactions?
Proteases cleave proteins, which can either inactivate them or activate them by processing latent forms into biologically active forms.
Why is proteolytic activation considered a rapid response mechanism?
It is faster to activate a latent protein via proteolysis than to synthesize a new protein through transcription and translation.
Name three families of proteases involved in latency and activation discussed in the lecture.
- Proprotein convertases (PCSKs)
- Matrix metalloproteases (MMPs)
- Secretases
What is the role of propeptides in protein activation?
Propeptides need to be cleaved for activation, aiding in proper folding and ensuring proteins are activated only when necessary.
What is the difference between constitutive and regulated secretory pathways?
• Constitutive pathway: Directly delivers cargo to the plasma membrane.
• Regulated pathway: Stores cargo in vesicles and releases it in response to specific signals.
How do PCSKs contribute to hormone maturation?
PCSKs cleave prohormones like proinsulin into their active forms, enabling their biological function.
What role does PCSK9 play in cholesterol metabolism?
PCSK9 promotes LDL receptor degradation in lysosomes, reducing the number of receptors on the plasma membrane and decreasing LDL clearance from circulation.
How do viruses exploit PCSKs for cell entry?
Viruses like SARS-CoV-2 use PCSKs such as furin to cleave glycoproteins, altering protein conformation and facilitating viral entry into host cells.
What is the significance of the furin cleavage site in the SARS-CoV-2 spike protein?
The furin cleavage site enhances viral entry by enabling better binding to the ACE2 receptor, contributing to higher virulence compared to SARS-CoV-1.
What is the ‘cysteine switch mechanism’ in matrix metalloproteases (MMPs)?
The propeptides of MMPs coordinates with a zinc ion to keep the enzyme inactive until cleavage removes the propeptides, activating the enzyme.
Name a key role of matrix metalloproteases (MMPs) in cancer progression.
MMPs facilitate tumour growth and metastasis by degrading the extracellular matrix, promoting angiogenesis, and enabling tumour invasion.
What is the role of secretases in Alzheimer’s disease?
Beta and gamma secretases cleave amyloid precursor protein, forming amyloid-beta peptides, which aggregate into plaques associated with Alzheimer’s pathology.
How can PCSK9 inhibitors be used therapeutically?
PCSK9 inhibitors increase LDL receptor recycling to the plasma membrane, improving cholesterol clearance and treating hypercholesterolemia.
What are amyloid plaques and their relevance in Alzheimer’s?
Amyloid plaques are aggregates of amyloid-beta peptides, formed due to beta and gamma secretase activity, and are toxic to neurons.
What are proprotein convertases (PCSKs), and what is their primary function?
PCSKs are serine proteases involved in protein maturation, receptor recycling, and are exploited by pathogens for activation processes.
What are the typical cleavage site characteristics of PCSKs?
PCSKs cleave at sites containing 2-5 basic residues, primarily arginine and lysine, regulated by pH and calcium levels.
How does the cleavage of proproteins by PCSKs benefit viruses like HIV-1?
PCSKs cleave viral glycoproteins, such as glycoprotein 160 in HIV-1, enabling their activation and enhancing viral infectivity.
Describe the functional domains commonly found in PCSKs.
PCSKs typically have a signal peptide, a propeptides for auto-catalytic activation, a catalytic domain, and a P domain regulated by calcium.
How do matrix metalloproteases (MMPs) contribute to tissue remodelling?
MMPs degrade components of the extracellular matrix, facilitating processes like wound healing, morphogenesis, and inflammation.
What is the role of MMP-2 and MMP-9 in late-stage prostate cancer?
These MMPs activate pathways leading to extracellular matrix degradation and the production of soluble RANKL, which promotes bone degradation.
How are MMPs activated from their latent forms?
The propeptides of MMPs is removed, disengaging the zinc ion from the catalytic site, which activates the enzyme—a process called the cysteine switch.
Why are MMP inhibitors important in clinical research?
MMP inhibitors target the catalytic zinc site, aiming to block extracellular matrix degradation in diseases like cancer and inflammatory disorders.
What is a key pathological role of gamma secretases in Alzheimer’s disease?
Gamma secretases generate amyloid-beta peptides, contributing to plaque formation in neuronal tissues, which are toxic to neurons.
What is the function of the ADAM family of proteins?
ADAM proteins are metalloproteases involved in cleaving membrane-anchored proteins, regulating pathways such as TNF-alpha and growth factor signalling.
What therapeutic strategies target secretases in Alzheimer’s disease?
Inhibitors of beta and gamma secretases are developed to reduce amyloid-beta plaque formation and mitigate neurotoxicity.
How does SARS-CoV-2 exploit furin (PCSK3) for cell entry?
Furin cleaves the spike protein of SARS-CoV-2, enabling conformational changes that enhance binding to ACE2 receptors and viral entry into cells.
Compare SARS-CoV-1 and SARS-CoV-2 in terms of furin cleavage sites.
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.
Why is the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein significant?
The RBD interacts with ACE2 receptors, and furin cleavage facilitates its ‘standing up’ conformation for efficient receptor binding.
What is a secretagogue?
A secretagogue is a substance that triggers the secretion of another substance, often playing a role in regulated pathways of vesicular exocytosis.
How do secretases contribute to protein shedding?
Secretases cleave membrane-bound proteins, releasing their extracellular domains to regulate processes like growth factor activation and receptor signalling.
What are intramolecular chaperones, and what is their role in proteolytic activation?
Intramolecular chaperones are parts of propeptides that assist in the correct folding of proteins during latency, ensuring proper conformation for activation.
Describe the process of protein sorting through the Golgi apparatus.
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.
What is the role of pre-peptides in protein synthesis?
Pre-peptides, also known as signal peptides, guide newly synthesized proteins into the endoplasmic reticulum and are cleaved off during protein maturation.
How do PCSKs recognize and cleave their substrates?
PCSKs recognize specific sequences around cleavage sites, typically with 2-5 basic residues like arginine and lysine, to cleave propeptides and activate proteins.
What is the significance of tissue-specific expression of PCSKs?
Tissue-specific PCSK expression allows tailored activation of proproteins, such as hormones or enzymes, to meet the distinct functional needs of different tissues.
Explain the role of PCSK1 and PCSK2 in hormone maturation.
PCSK1 and PCSK2 process prohormones like proinsulin into active forms, ensuring proper folding and functionality of hormones within regulated secretory pathways.
Why is the production of polyproteins advantageous for cells?
Polyproteins allow the efficient synthesis of multiple proteins from a single gene, saving energy and enabling coordinated regulation of protein production.
What roles do MMPs play in wound healing?
MMPs degrade and remodel the extracellular matrix, clearing damaged tissue and promoting cell migration and angiogenesis necessary for wound repair.
How does MMP dysregulation contribute to cancer progression?
Dysregulated MMPs enhance tumour invasion, metastasis, and angiogenesis by breaking down the extracellular matrix and modifying the tumour microenvironment.
What is the function of ADAM17 in cellular signalling?
ADAM17 cleaves membrane-bound proteins like TNF-alpha precursors, releasing their active forms and regulating inflammatory and immune responses.
How do beta and gamma secretases differ in processing amyloid precursor protein (APP)?
• 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.
How does the SARS-CoV-2 spike protein remain infectious after furin cleavage?
The cleaved portions of the spike protein remain non-covalently bound, altering the conformation to facilitate binding to ACE2 receptors and enhancing infectivity.
What is the cysteine switch mechanism in MMPs?
The cysteine in the propeptides domain coordinates with the zinc ion, keeping MMPs inactive until cleavage disrupts this interaction, activating the enzyme.
What makes secretases a therapeutic target in Alzheimer’s disease?
Inhibiting beta and gamma secretases can reduce amyloid-beta production, potentially slowing plaque formation and neurotoxicity in Alzheimer’s patients.
Why are MMP inhibitors challenging to develop as drugs?
MMP inhibitors often fail in clinical trials due to off-target effects and difficulty achieving selective inhibition of specific MMPs without affecting others.
What distinguishes regulated from constitutive secretory pathways?
Regulated pathways store vesicles until specific signals trigger secretion, while constitutive pathways continuously deliver contents to the plasma membrane.
Describe the process of LDL receptor recycling and PCSK9’s involvement.
LDL receptors are normally recycled to the plasma membrane after LDL dissociation, but PCSK9 directs them to lysosomes for degradation, reducing LDL clearance.
How does furin cleavage enhance SARS-CoV-2 virulence compared to SARS-CoV-1?
SARS-CoV-2’s furin cleavage site enables better spike protein activation and ACE2 receptor binding, increasing its ability to infect human cells.
What is the role of soluble RANKL in late-stage prostate cancer?
Soluble RANKL, produced by MMP7 cleavage, promotes bone degradation, contributing to the osteolytic effects seen in advanced prostate cancer.
Why is early-onset Alzheimer’s linked to mutations in presenilin proteins?
Mutations in presenilin proteins, components of gamma secretase, increase catalytic activity, leading to overproduction of amyloid-beta peptides and early plaque formation.
