Mechanisms of Protein-Folding Diseases

Flashcards covering key concepts related to mechanisms of protein-folding diseases, including causes, cellular responses, specific disease examples, and therapeutic insights, based on the provided lecture notes.

What is the fundamental problem underlying many pathological conditions related to cellular function and integrity?

The protein-folding problem, where proteins must achieve their proper conformation and location within the cell.

What are the five examples of protein-misfolding events described that can lead to disease?

Improper degradation, mislocalization, dominant-negative mutations, structural alterations that establish novel toxic functions, and amyloid accumulation.

What cellular systems are required for correct protein folding and for destroying improperly folded proteins?

Multiple chaperone systems are required to fold proteins correctly, and degradation pathways destroy improperly folded proteins.

How do protein mutations contribute to misfolding diseases?

Mutations cause misfolded, nonfunctional forms of proteins to accumulate.

What makes protein folding in vivo challenging?

The crowded environment of the cell and constant bombardment by high-energy collisions with neighboring proteins.

What are the two major cellular responses to the accumulation of unfolded proteins?

The unfolded protein response (UPR) in the ER and the heat-shock response (HSR) in the nuclear and cytosolic compartments.

What is the role of the proteasome, autophagy, and ER-associated degradation (ERAD) in protein homeostasis?

They are deployed to degrade misfolded proteins that cannot be properly refolded.

What was the first inherited human disease with a known molecular mechanism linked to protein misfolding?

Sickle cell anemia.

How does the single point mutation in sickle cell anemia lead to disease?

A single point mutation changes glutamic acid to valine in the β-globulin chain of hemoglobin, exposing a hydrophobic patch that causes polymerization in deoxygenated environments.

How can improper degradation cause disease, even if a mutant protein retains some functionality?

Cellular degradation systems can be overactive, destroying proteins that are mutant but still partially functional, leading to more severe disease.

What is the common causative mutation in cystic fibrosis (CF)?

Deletion of a phenylalanine residue at position 508 (ΔF508) in CFTR, leading to its misfolding and degradation.

How might inhibition of chaperone systems be therapeutically beneficial for cystic fibrosis patients with the ΔF508 mutation?

Disrupting some chaperone systems (like AHA1) can allow mutant CFTR to escape degradation, become more stable, and partially functional.

What is Gaucher's disease caused by?

Mutations in β-glucosidase, a lysosomal enzyme, leading to defects in lipid metabolism and intracellular accumulation of its substrate.

What is a potential therapeutic strategy for Gaucher's disease related to protein folding?

Upregulation of chaperones that assist in the correct folding of β-glucosidase, or using 'pharmacological chaperones' that stabilize the enzyme's fold.

How do 'pharmacological chaperones' work in conditions like Gaucher's disease?

They directly bind to the mutant enzyme, stabilizing its fold and allowing it to reach its site of activity, where the physiological substrate displaces the chaperone and the enzyme becomes active.

How can improper localization of a protein cause disease?

Mutations that destabilize correct folding can lead to the protein being trafficked incorrectly, resulting in loss of function at its proper location and/or gain-of-function toxicity if it accumulates in a wrong location.

What dual toxicity is observed in α1-antitrypsin deficiency caused by protein misfolding?

Recessive loss-of-function (emphysema due to lack of protease inhibition in lungs) and dominant gain-of-function (liver damage due to accumulation of misfolded protein in the ER of hepatocytes).

What therapeutic approach has shown promise in alleviating α1-antitrypsin-induced hepatic toxicity?

Drugs that enhance autophagy, such as rapamycin and carbamazepine, because aggregates in the liver are degraded by macroautophagy.

What is a dominant-negative mutation?

A mutation where the mutant protein antagonizes the function of the wild-type protein, causing a loss of protein activity even in a heterozygote.

How do dominant-negative mutations in keratin proteins (KRT5, KRT14) cause epidermolysis bullosa simplex?

The mutant keratin misfolds and aggregates, compromising the function of the entire intermediate filament structure, even when wild-type protein is present, leading to severe blistering.

What is 4-phenylbutyrate (4-PBA) and how does it act as a potential therapy for epidermolysis bullosa simplex?

4-PBA is a chemical chaperone that can cause the degradation of aggregated keratin, possibly by increasing the cellular concentration of protein chaperones like HSP70.

Why are mutations in the transcription factor p53 significant in cancer?

p53 mutations are common genetic alterations in cancer, leading to far-reaching effects due to its role in regulating genome integrity pathways (apoptosis, DNA repair, cell cycle).

How does mutant p53 act in a dominant-negative manner in cancer?

Even if a wild-type p53 copy is present, mutant p53 can associate with other p53 monomers to form dysfunctional tetramers, making it unlikely for functional wild-type tetramers to form.

What are Nutlins and how do they work in cancer therapy?

Nutlins are small molecules that prevent MDM2 from interacting with and promoting degradation of wild-type p53, thereby increasing the probability of forming functional wild-type p53 tetramers.

What is an example of a gain-of-toxic-function protein misfolding disease?

Apolipoprotein E (APOE4) in Alzheimer's disease.

How does the APOE4 allele contribute to Alzheimer's disease pathogenesis?

The APOE4 polymorphism stabilizes an altered conformational fold with an extra salt bridge, which disrupts mitochondrial function, impairs neurite outgrowth, and is associated with increased levels of Aβ peptide.

How do oncogenic proteins, like v-SRC, often rely on chaperone systems?

Many oncogenic kinases require assistance from the HSP90 chaperone machinery to acquire their mature fold, localize correctly, avoid degradation, and exert their malignant phenotypes, highlighting HSP90 as a therapeutic target.

What are amyloid fibers and what role do they play in disease?

Amyloid fibers are insoluble fibrous protein aggregates that accumulate and contribute to a variety of diseases, ranging from neurodegenerative disorders to systemic amyloidoses.

What is the current understanding of the toxicity of amyloid in neurodegenerative diseases?

Lower-order oligomers are frequently posited as being responsible for disrupting cellular functions, with amyloid deposits possibly acting as a protective mechanism to sequester these toxic species, though amyloid itself may also contribute to disease spread.

What is a general therapeutic strategy for diseases involving amyloid accumulation?

Targeting amyloid folds in general, potentially with antibodies that recognize common amyloid fibrils and toxic oligomers, or small molecules that prevent aggregate formation or enhance their degradation.

How has knowledge of transthyretin (TTR) misfolding informed drug development for familial amyloid polyneuropathy (TTR-FAP)?

Understanding that point mutations destabilize the TTR tetramer, leading to monomer accumulation and amyloid formation, led to strategies to stabilize the tetramer using small molecules that bind to its thyroxine-binding site.