Chaperons

1. Molecular Chaperones in Plant
Stress Management.
Pragati Randive
Reg No: 0025
Jr. M.Sc. (Ag. Biotechnology)

2. Presentation outline
 Background
 Introduction
 Heat Shock Proteins/Chaperones
HSP 70 Family;
HSP 60 (Gro EL and chaperonins);
HSP 90 family;
HSP 100(Clp) family;
small (sHS) family
 HSP/Chaperone Network
 Cross-talk between HSPs/chaperones and other
stress response mechanisms
 Schematic representation of the HSP/HSF pathway
 References

3. Background
Sequence of Events Occurring in Plants Due to High Temperature.
At cellular Level:
High Temperatures alter lipid properties causing membranes to become more fluid
and thereby disrupting membrane processes.
Alteration in enzyme activity leading to imbalance in metabolic pathways and
eventually Protein Denaturation.
Membrane and protein damage leads to the production of Active Oxygen
Species(AOS), resulting in heat–induced oxidative damage .
At Physiological level:
This damage translates into reduced efficiency of photosynthesis, impaired
translocation of assimilates and loss of carbon gain.
These factors in turn combine to cause altered phenology, reproductive failure and
accelerated senescence.

4. Introduction
• As abiotic stresses usually cause protein dysfunction, maintaining proteins in
their functional confirmations and preventing the aggregation of non-native
proteins are particularly important for cell survival under stress.
• Molecular Chaperones are special proteins that help in correct folding of
proteins during post-translational processing of proteins.
• Heat Shock Proteins(HSPs) functioning as molecular chaperones are the key
components responsible for protein folding, assembly, translocation and
degradation under stress conditions and in many normal cellular processes.
• There are 5 well-characterized classes of HSPs:
-the HSP 70(DnaK) family;
-the HSP 60 (Gro EL and chaperonins)
-the HSP 90 family;
-the HSP 100(Clp) family;
-the small (sHS) family.

5. Hsp70 family
• Hsp70 chaperones, together with their co-chaperones (e.g. DnaJ/Hsp40 and GrpE),
assist with a wide range of protein folding processes.
• Prevent aggregation and assist in refolding of non-native proteins under both normal and
stress conditions.
• Constitutively expressed Hsp70 family members ,referred to as Hsc70 (70-kDa heat-
shock cognate) are involved in assisting the folding of de novo synthesized polypeptides
and the import/translocation of precursor proteins.
• Other family members are expressed only when the organism is challenged by
environmental assaults. Therefore, they are more involved in facilitating refolding and
proteolytic degradation of unstable proteins by targeting the proteins to lysosomes or
proteasomes.
• In addition, some members of Hsp70 are involved in controlling the biological activity of
folded regulatory proteins, and might act as negative repressors of heat-shock factor
(HSF) mediated transcription.

6. Chaperonins (Hsp60)
• Hsp60; the term chaperonin was first suggested to describe a class of molecular
chaperones that are evolutionarily homologous to E. coli GroEL.
• Chaperonins are a class of molecular chaperones found in prokaryotes and in the
mitochondria and plastids of eukaryotes (e.g.prokaryotic GroEL and the eukaryotic
equivalent Hsp60).
• This class Hsp60 is also important in assisting plastid proteins such as Rubisco.
• These Hsps60 bind different types of proteins after their transcription and before folding to
prevent their aggregation.
• Functionally, plant chaperonins are limited and stromal chaperones (Hsp70 and Hsp60)
are involved in attaining functional conformation of newly imported proteins to achieve
their native forms in the chloroplast.
Source: Plant heat-shock proteins: A mini review. -Mohamed H. Al-Whaibi

7. Hsp90 family
• HSP90 is the most abundant in cytosolic heat shock protein family in both eukaryotic
and prokaryotic cells and is rapidly induced in response to various stress conditions.
• Under physiological conditions, HSP90 associates with various intracellular proteins,
including calmodulin, actin, tubulin, kinases, and receptor proteins.
• The major role of Hsp90 is to manage protein folding but it also plays a key role in
signal-transduction networks, cell-cycle control, protein degradation and protein
trafficking .
• This class, also, plays another important role as they regulate the cellular signals
such as the regulation of glucocorticoid receptor (GR) activity.
• Cytoplasmic Hsp90 is responsible for pathogen resistance by reacting with resistance
protein (R) which is the signal receptor from the pathogen.

8. Hsp100/Clp family
• One unique function of this class is the reactivation of aggregated proteins by
resolubilization of non-functional protein aggregates and also helping to degrade
irreversibly damaged polypeptides.
• HSP100 chaperones are essential components of the protein quality control (PQC)
process. They act in concert with HSP70 chaperones to thread and degrade toxic
protein aggregates.
• They are also involved in protein targeting as they process the signal peptide of
specific precursor proteins once they have reached their destination.

9. sHSPs
• Plant sHsps respond to a wide range of environmental stresses, including heat, cold,
drought, salinity and oxidative stress.
• One of the characteristic functions of this class is the degradation of the proteins that
have unsuitable folding.
• The sHsps cannot refold non-native proteins, but they can bind to partially folded or
denatured substrates proteins, preventing irreversible unfolding or wrong protein
aggregation.
• Recently in a review (Nakamoto and Vı´gh, 2007) it was concluded that there were
some indications that small heat shock proteins play an important role in membrane
quality control and thereby potentially contribute to the maintenance of membrane
integrity especially under stress conditions.

10. Table : Summary of HSPs in plant immunity
Source: MINI-Review :Heat Shock Proteins: A Review of the Molecular Chaperones for Plant Immunity

11. HSP Response to Stress

12. Figure 1 Simple illustration of part of the chaperone machines that operate in the cytosol
Source: Plant heat-shock proteins: A mini review. -Mohamed H. Al-Whaibi

13. HSP/Chaperone Network
Figure 1. The heat-shock protein (Hsp) and chaperone network in the abiotic
stress response.
Source :Review: Role of plant heat-shock proteins and molecular chaperones in the abiotic stress response.

14. Fig: Suggested cross-talk between the heat shock protein (Hsp)/chaperone network and other stress-
response mechanisms in plants.
Cross-talk between HSPs/chaperones and other stress
response mechanisms
Source :Review: Role of plant heat-shock proteins and molecular chaperones in the abiotic stress response.

15. Molecular regulatory mechanism of
heat shock proteins
Fig: Schematic diagram showing the molecular regulatory mechanism of
heat shock proteins based on a hypothetical cellular model.
Source: Review: Physiological, Biochemical, and Molecular Mechanisms of Heat Stress Tolerance in Plants

16. Schematic representation of the HSP/HSF
pathway
Source: Review article: The heat-shock protein/chaperone network and multiple stress resistance

17. • Wangxia Wang, Basia Vinocur, Oded Shoseyov and Arie Altman.(2004)
Review:Role of plant heat- shock proteins and molecular chaperones in the abiotic stress response.
TRENDS in Plant Science Vol.9 No.5 May 2004
• Chang-Jin Park and Young-Su Seo.(2015)
MINI-Review :Heat Shock Proteins: A Review of the Molecular Chaperones for Plant Immunity .
Plant Pathol. J. 31(4) : 323-333 (2015)
• Pierre Jacob, Heribert Hirt,and Abdelhafid Bendahmane.(2017)
Review article: The heat-shock protein/chaperone network and multiple stress resistance
Plant Biotechnology Journal (2017), pp. 1–10
• Mirza Hasanuzzaman ,Kamrun Nahar ,Md. Mahabub Alam ,Rajib Roychowdhury and Masayuki Fujita
Review: Physiological, Biochemical, and Molecular Mechanisms of Heat Stress Tolerance in Plants.
Int. J. Mol. Sci. 2013, 14(5), 9643-9684
 References