1. HEAT SHOCK PROTIENS
- Purvi Shah

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. Structural Levels of Proteins
Primary Secondary

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. Protein Denaturation with
extreme pH or Temp.

6. Temp
environ
Temp
cell
Folded
Proteins
Unfolded
Proteins Aggregates
Loss of Protein
Function
Network
failure
Death
Cell

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. 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. 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. 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

12. 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

13. 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.

14. 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

15. HSP70 works with HSP40 to capture and transfer misfolded client proteins to prefoldin and other chaperonins for refolding

16. HSP60
 14-16 monomer
 ATP
 GroES and GroEL
 mediate the native folding of proteins through
cooperation of HSP70 and 60

18. 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

19. 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

20. 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.

21. Why Don't Heat Shock Proteins
Denature?
Better Hydrogen Bonds
Better Hydrophobic Internal Packing
Enhanced Secondary Structure
Helix Dipole Stabilization

22. Protein denaturation by
temperature