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Heat shock proteins


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Heat shock proteins

  1. 1. HEAT SHOCK PROTIENS - Purvi Shah
  2. 2. Proteins are the major components of living organisms and perform a wide range of essential functions in cells Proteins regulate metabolic activity, catalyze biochemical reactions and maintain structural integrity of cells and organisms Proteins
  3. 3. Structural Levels of Proteins Primary Secondary
  4. 4. Protein Denaturation  The activity of a protein depends on its three-dimensional structure.  Intramolecular bonds, especially hydrogen bonds, maintain the structure.  Hydrogen bonds may break when the pH drops or the temperature rises above normal denaturing the protein
  5. 5. Protein Denaturation with extreme pH or Temp.
  6. 6. Temp environ Temp cell Folded Proteins Unfolded Proteins Aggregates Loss of Protein Function Network failure Death Cell
  7. 7. Interesting story F. Ritossa –1960 discovered the heat shock (HS) response while observing the salivary cells of Drosophila and named them HSP’s My name is Chaperone
  8. 8. How do Chaperones work?  One major function of chaperones is to prevent both newly synthesised polypeptide chains and assembled subunits from aggregating into nonfunctional structures  High temperatures and other stresses, such as altered pH and oxygen deprivation, make it more difficult for proteins to form their proper structures and cause some already structured proteins to unfold  Heat Shock Proteins are induced rapidly at high levels to deal with this problem
  9. 9. Different Types of Heat Shock Proteins Heat Shock Proteins are classified by their molecular weight, size, structure, and function. They are divided into several families, namely - 1. HSP100 2. HSP90 3. HSP70 4. HSP60 (chaperonin) 5. Small Heat Shock Proteins/ (alpha)-crystalline proteins
  10. 10. HSP100 Functions -solubilizes protein aggregates thereby dissociating them -facilitates proteolysis -essential in yeast for acquired thermotolerance -essential for yeast prion propagation  6-7 monomer  ATP  no co-chaperon is required
  11. 11. HSP 90 stabilizes proteins prior to complete folding or activation forms stable complexes with inactive glucocorticoid receptor and other transcription factors most abundant non-ribosomal protein (cytosolic version) most abundant protein in endoplasmic reticulum (ER version)  dimer  ATP  HoP and p23
  12. 12. HSP90 interacts with HSP40, HSC70/HSP90 organizing protein (HOP), and co-chaperones to bind and stabilize newly synthesized substrate/client proteins. This ATPregulated cycle of substrate binding is critical to the activation of many oncogenic signaling molecules.
  13. 13. HSP70  monomer  ATP  DnaJ and GrpE  assists in protein transport into mitochondria and the endoplasmic reticulum  protects proteins under stress  stabilizes proteins prior to complete folding  transports across membranes and proteolysis
  14. 14. HSP70 works with HSP40 to capture and transfer misfolded client proteins to prefoldin and other chaperonins for refolding
  15. 15. HSP60  14-16 monomer  ATP  GroES and GroEL  mediate the native folding of proteins through cooperation of HSP70 and 60
  16. 16. A) Reconstruction of the GroEL structure with and without the GroES ™lid∫ from cryoelectron microscopy pictures. B) Model of the GroEL chaperone cycle. Two misfolded proteins (green and blue) are simultaneously folded in a phase-shifted manner. The red circles symbolize the hydrophobic substrate binding sites of GroEL
  17. 17. sHsp  8-24 monomer  exhibit chaperone activity in vitro and thermoprotection in vivo  produced at significant levels in cells experiencing heat stress  most are heat inducible, but some are synthesized in unstressed conditions-such as for cell development
  18. 18. Denatured or unfolded substrates bind to the hydrophilic surface of small HSP complexes and prevent the substrate from aggregating.The substrate either stays sequestered or is released to be refolded or degraded.
  19. 19. Why Don't Heat Shock Proteins Denature? Better Hydrogen Bonds Better Hydrophobic Internal Packing Enhanced Secondary Structure Helix Dipole Stabilization
  20. 20. Protein denaturation by temperature