Class 11: Protein Folding-agbas

Question 1

Molecular chaperons

Cellular quality control system: Proteosomes, autophagy, ERAD (ER-asso. Degradation)

Answer 1

Maintenance of protein homeostasis=critical

Question 2

5 main mechanisms of toxicity in cell:

Answer 2

Improper degradation

Improper localization

Dominant negative mutations

Gain-of-toxic function

Amyloid accumulation

Question 3

First known protein-misfolding Dz

Answer 3

Sickle cell anemia

Question 4

Single point mutation changes E (glu) to V (Val) in the beta-globulin chain of Hb

Exposing a hydrophobic patch that leads to polymerization

Reduces elasticity of RBC

Causes extreme pain, extensive tissue destruction, and anemia

Answer 4

Sickle cell anemia

Question 5

Overactive cellular degradation systems (ERAD and autophagy) can contribute the accumulation of mutant, misfolded, incomplete degraded proteins

This can contribute to the development of more severe Dz

Answer 5

Improper degradation

Question 6

ERAD

Answer 6

Endoplasmic reticulum asso. Degradation

Question 7

For proper trafficking to target organelles, the proteins must fold correctly

Incorrectly folded proteins lead to improper subcellular end point
Leads to:
Loss of function and gain of function-toxicity.

Answer 7

Improper localization

Question 8

A mutant protein antagonizes the function of the WT protein

• loss of protein activity
• mutant protein presence interferes the function of the WT protein at cellular and structural levels

Answer 8

Dominant negative mutations

Question 9

5 mechanisms of protein misfoldings leading to toxicity

Answer 9

Improper degradation
Improper localization
Dominant negative mutations 
Gain of toxic function 
Amyloid accumulation

Question 10

Protein conformational changes can cause dominant phenotypes

• Proteins become toxic
• -APOE4 disrupts mito. Function; impairs neurite outgrowth.
• -Cu/Zn-superoxide dismutase (SOD1)
• -Src kinases in CA

Answer 10

Gain of toxic function

Question 11

• Insoluble protein aggregates
• have VQIVY sequence
• lower order oligomers cause toxic effect; deposition could be a protective mechanism
• several amyloidogenic proteins form pore-like structure which disrupts the cell membrane integrity.
• misfolded forms of the protein are frequently observed in: the elderly(natural aging) and individuals w/ mutations in the protein early in life

Answer 11

Amyloid accumulation

Question 12

how amyloid progress to amyloid plaques?

Answer 12

1. seeding (nucleation)
2. Fibrin formation
3. Deposit

Question 13

Why is knowledge about protein folding significant?

Answer 13

Opens new avenues for Rx discovery

Question 14

Common amyloidogenic preotein

Primary carrier of hormone thyroxine and a retinol transporter

Answer 14

TTR

Transthyretin (protein)-4 identical polypeptides

Question 15

How can Rx potentially remediate blocking the aggregate formation?

Answer 15

1. Small molecules can act as stabilizer
2. site-specific antibodies
   - recognize conformational changes
   - can be sequence specific(VQIVY)

Question 16

Organism maintains its capacity to grow and reproduce

Ketones for environmental stressors (DRA)

Intrinsic induction of stress defense programs and resulting adaptation can increase life expectancy

Answer 16

Rxn to stress and adaptive response

Question 17

Keystones for environmental stressors:

DRA

Answer 17

To Detect
To Resp
To adopt

Question 18

How can hermetic stress affect protein folding?

Answer 18

Applying moderate levels of stress could trigger beneficial and adaptive stress defense pathways, allowing longer life

Caloric restriction prolongs the lifespan

Question 19

Maintenance of protein homeostasis

Cellular and organismal functionality req’s: protein production,folding, and degradation

Unfolded protein responses (UPR)

Complex pathways to ensure protein homeostasis in different compartments

• CYTOSOL
• ER(UPR)
• MITO. (UPR)
• -more recently discovered;complex relationship btw nucleus and mito.

Answer 19

Proteostasis

Question 20

Methods of proteostasis:

Answer 20

• Cellular proteins folded by chaperons
• membrane and secreted proteins fold and mature in ER
• specific response help to cope w/ misfolded proteins accumulation
• apoptotic pathway is the last line of defense
• Heat shock response (HSR)
• UPR-ER is mediated; inositol req’ing element 1 (IRE1),PERK, ATF6

Question 21

Manages denatured proteins into the cytosol (HSF1)

Answer 21

Heat shock response (HSR)

Question 22

Composed of ~1500 proteins.
Encoded by both nuclear and mito. Genome.
13 essential proteins of ETC are encoded by mtDNA.
2 major mito. Chaperon systems 70 and 60-10.
Protein quality control (PQC) proteases; specific each mito. Compartment. Recognize and degrade the proteins dont fold and properly assembled.

Answer 22

UPR-mito. Senses the overload of the QC system capacity

-activates the transcription of nuclear encoded protective genes; re-establish the mito. Homeostasis

Question 23

• The signal transmission from the unfolded/misfolded mito. Proteins to the nucleus cannot be accomplished using HSR and UPR-er system.
• the best described system is the retrograde response (RTG)-metabolic adaptations in response to decreased mito. Activity in yeast.
• RTG doesnt modulate the mito-chaperons expression;UPR-mt has a distinct regulatory mechanism
• stochiometric imbalance among the ETC protein complexes (comp 1,3,4,5) activates UPR-mt system

Answer 23

UPR-mt signaling