Plants experience various stresses like temperature, drought, and pathogens. Stress can cause protein denaturation which is prevented by heat shock proteins (Hsps). Hsps maintain protein structure during stress. There are five classes of Hsps in plants based on molecular weight including Hsp100, Hsp90, Hsp70, Hsp60, and small Hsps. Hsps act as molecular chaperones to refold proteins, prevent aggregation, and facilitate protein transport. Heat stress transcription factors regulate Hsp gene expression, leading to increased Hsp synthesis during stress.

1. Presented by
Dhanuja N
2019508005
Heat shock proteins

2. Stress
 Plants interact with not only climatic factors (such
as irradiation, temperature, and drought) but also
soil factors (such as salinity) and biotic factors
(such as herbivores and pathogens). All these
factors put the plant under interrelated stresses.
 Plants could not change their sites to avoid such
stresses, but have different ways and
morphological adaptations to tolerate these
stresses

3. What happens during stress?
 Proteins are the major
components of living
organisms and perform a
wide range of essential
functions in cells.
 The activity of a protein
depends on its 3D
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.

4. Heat-shock proteins
 Heat stress as well as other stresses can trigger
some mechanisms of defense such as the
obvious gene expression that was not expressed
under “normal” conditions.
 The sudden changes in genotypic expression
resulting in an increase in the synthesis of protein
groups. These groups are called “heat-shock
proteins” (Hsps), “Stress-induced proteins” or
“Stress proteins”

5. Heat-shock proteins
 Heat shock proteins (HSPs) are ubiquitous
proteins found in plant and animal cells.
 They originally were described in relation to heat
shock (Ritossa, 1962) in Drosophila but are now
known to be induced by a wide variety of
stresses, including exposure to cold, UV light,
wound healing, tissue remodeling, or biotic
stresses.
 Synthesis of these proteins is energy costly.

6. Hsp classification
 In plants, there are five principal classes of Hsps
characterized by their activities as molecular
chaperones according to their approximate
molecular weight
1. HSP100
2. HSP90
3. HSP70
4. HSP60 (chaperonin)
5. Small Heat Shock Proteins/ (alpha)-crystalline
proteins

7. Hsps of prokaryotes and
eukaryotes
Escherichia coli Eukaryotic cells
ClpB Hsp100
HtpG Hsp90
Dnak Hsp70
GroEL Hsp60

8. Functions

10. Heat stress transcription
factors
 Differenent classes of genes code for these
proteins.
 The transcription of these genes is controlled by
regulatory proteins called heat stress transcription
factors (Hsfs) located in the cytoplasm in an
inactive state.
 Each factor has one carboxylic terminal (C-
terminal) and three amino terminal (N-terminal)
and has the amino acid leucine.

11. These factors have been classified into three
classes
 Plant HsfA such as HsfA1 and HsfA2 in L.
esculentum
 Plant HsfB such as HsfB1 in L. esculentum
 Plant HsfC
In the absence of stressing factors, Hsfs are
present in the cytoplasm as single and free as there
is no binding activity with DNA, but when stress
starts the factors aggregate in triplet and
accumulate in the nucleus

12. Upregulation in stress
 During heat stress, outer membrane proteins
(OMPs) do not fold and cannot insert correctly
into the outer membrane. They accumulate in the
periplasmic space.
 These OMPs are detected by DegS, an inner
membrane protease, that passes the signal
through the membrane to the sigmaE
transcription factor.
 However, some studies suggest that an increase
in damaged or abnormal proteins brings HSPs
into action.

13. sHsps
 8-24 monomer.
 Exhibit chaperone activity in vitro and
thermoprotection in vivo.
 Produced at significant levels in cells under heat
stress.
 Most are heat inducible, but some are
synthesized in unstressed conditions-such as for
cell development.
 Activity is independent of ATP.
 Degradation of proteins that have unsuitable
folding by ubiquitination.

14. Hsp60
 Chapronins
 14-16 monomer
 ATP
 Mediate the native folding of proteins through
cooperation of HSP70 and 60
 Mediate folding and prevent aggregation of
proteins transported to chloroplast and
mitochondria.

15. Hsp 70
 Monomer
 ATP
 Assists in protein transport into mitochondria and
the endoplasmic reticulum
 Protects PS II during photoinhibition
 Stabilizes proteins prior to complete folding
 Transports across membranes and proteolysis

17. Hsp 90
 Dimer
 ATP
 Stabilizes proteins prior to complete folding or
activation
 Forms stable complexes with inactive
glucocorticoid receptor and other
 Most abundant non-ribosomal protein (cytosolic
version)
 Most abundant protein in endoplasmic reticulum
(ER version)

18.  Cytoplasmic Hsp90 is responsible for pathogen
resistance by reacting with resistance protein (R)
which is the signal receptor from the pathogen.
 Hsp90 was an essential component of innate-
immune response and pathogenic resistance in
rice.

19. Hsp 100
 6-7 monomer
 ATP
 No co-chaperon is required
Functions
 Solubilizes protein aggregates thereby
dissociating them
 Facilitates proteolysis
 Essential in yeast for acquired thermotolerance
 Essential for yeast prion propagation

20. Hsp Families Cellular location Proposed functions
Hsp27 (sHsp) Cytosol, nucleus
Microfilament stabilization,
antiapoptotic
Hsp60 Mitochondria
Refolds proteins and
prevent aggregation of
denatured proteins,
proapoptotic
Hsp70 Antiapoptotic
• Hsp72(Hsp70
)
Cytosol, nucleus
Protein folding,
cytoprotection
• Hsp73(Hsc70
)
Cytosol, nucleus Molecular chaperones
• Hsp75(mHsp
70)
Mitochondria Molecular chaperones
• Hsp78(GRP7
8)
Endoplasmic
reticulum
Cytoprotection, molecular
chaperones
Hsp90
Cytosol,
endoplasmic
Regulation of steroid
hormone receptors, protein

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

22. Conclusion
 The expression of Hsps could occur in natural
environment.
 The hsp genes are found in all species but they
vary in patterns of expression.
 The expression of Hsps could be correlated with
resistance to stress.
 The threshold of species for Hsps expression are
correlated with the strength of stress prevailing in
the environment.

23. References
 Chang-Jin Park and Young-Su Seo, Heat Shock
Proteins: A Review of the Molecular Chaperones
for Plant Immunity, Plant Pathol J. 2015 Dec;
31(4): 323–333.
 Mohamed H.Al-Whaibi, Plant heat-shock proteins:
A mini review, Journal of King Saud University –
Science, Volume 23, Issue 2, April 2011, Pages
139-150.
 https://en.wikipedia.org/wiki/Heat_shock_protein
 https://www.ncbi.nlm.nih.gov/pubmed/18432918