This document discusses different types of chaperone proteins. It begins by explaining that chaperones assist other proteins in folding correctly by interacting with unfolded or misfolded proteins. The main types discussed are molecular chaperones like Hsp70 and Hsp90, and chaperonins. Hsp70 binds to hydrophobic regions of unfolded proteins to prevent aggregation, while Hsp90 helps activate client proteins. Chaperonins form folding chambers and there are two groups - group 1 found in prokaryotes and organelles, and group 2 in eukaryotes and archaea. Specific examples of chaperone homologs in different organisms are also provided.

1. CHAPERONES
ANJU ANTHARJANAM V.S.
DEPARTMENT OF BIOCHEMISTRY
UNIVERSITY OF KERALA
KARIAVATTOM CAMPUS

2. INTRODUCTION
• The three dimensional conformation of proteins
is important for their biological functions. so how
polypeptide chains ultimately fold into their final
conformation is also an important topic.
• Some of the proteins can spontaneously generate
the correct functionally active conformation.
• However a vast majority of proteins can attain
correct conformation only through the assistance
of certain proteins referred to as chaperones.
2avs

3. CHAPERONES
• Chaperones are proteins that interact with unfolded,
partially folded or improperly folded polypeptides
facilitating correct folding pathways or providing
microenvironments in which folding can occur.
• The chaperones are evolutionary conserved.They are
found in all organisms from bacteria to humans and
some are homologs with high sequence similarity that
use almost identical mechanisms to assist protein
folding.
• Chaperones have ATPase activity (binding,hydrolysis
and exchange of ATP essential for their function).
3avs

4. Types of chaperones
CHAPERONES
MOLECULAR
CHAPERONES
• Hsp 70
• Hsp 90
CHAPERONINS
• Group 1
• Group 2
4avs

5. Some chaperone homologs and their location
 Hsp 60 (chaperone 60 family)
 GroEL in bacterial cytosol
 Hsp 60 in mitochondrial matrix
 RubisCo binding protein in chloroplasts
 Hsp 70(stress70) proteins
 Hsp 70 in mammalian cytosol
 Bip in ER of eukaryotes
 Grp 75 in mitochondria
 DnaK in bacterial cytosol
 Hsp 90(stress 90) proteins
 Hsp 83 in eukaryotic cytosol
 Grp 94 in mammalian ER
 Htgp in bacterial cytosol
avs 5

6. Molecular chaperones
Hsp 70 &Hsp 90
• They bind to a short segment of a protein
substrate and stabilize unfolded or partly folded
proteins thereby preventing these proteins from
aggregating and being degraded.
• Hsp 70 family
• The heat shock protein Hsp 70 (Hsp-heat shock
protein,70-ml.wt-70,000)and its homologs are
the major chaperones in all organisms.
• They were first identified by their rapid
appearance after a cell has been stressed by heat
shock.
6avs

7. Molecular chaperones cntd..
• Hsp 70 proteins bind to regions of unfolded
polypeptides that are rich in hydrophobic
residues,preventing inappropriate
aggregation.
• Hsp 70 proteins also block the folding of
certain proteins that must remain unfolded
until they have been translocated across a
membrane.
7avs

8. • The Hsp 70 proteins bind to and release
polypeptides in a cycle that uses energy from ATP
hydrolysis and involves several other co-
chaperones.
• Co-chaperones
• Hsp 40 in eukaryotes and DnaJ in bacteria help to
increase efficiency of Hsp 70 mediated folding of
many proteins by stimulating substrate binding
and hydrolysis of ATP.
• Other examples are GrpE(in bacteria),BAG,HspBP
and Hsp 110(in eukaryotes).
8avs

9. 9avs

10. • Hsp 90 family
• They are present in all organisms except archaea.
• They ensure the activation and functional regulation of
of their substrates usually called ‘clients’.
• Hsp 90 function as a dimer in a cycle in which ATP
binding ,hydrolysis,and ADP release are coupled to
conformational changes and to binding,activation,and
release of clients.
• Hsp 90s can help cells recognize misfolded proteins
that are unable to refold and facilitate their
degradation.
10avs

11. 11avs

12. CHAPERONINS
• They form small folding chambers into which all
or part of an unfolded protein can be
sequestered giving it time and an appropriate
environment to fold properly.
• They are also called Hsp 60s.
• They are huge cylindrical supramolecular
assemblies formed from two rings of oligomers.
• There are two distinct groups of chaperonins-
Group 1 and Group 2 that differ in their
structures,molecular mechanism and locations.
12avs

13. Two classes of chaperonins:
Group 1
• Found in prokaryotes,
chloroplasts and
mitochondria.
• Composed of two rings,
each having seven subunits
that interact with a
homoheptameric co-
chaperone lid.
• GroEL/GroES in bacteria.
Group 2
• Found in the cytosol of
eukaryotic cells and in
archaea.
• Can have 8 to 9 either homo-
or hetero- meric subunits in
each ring.
• Lid function is incorporated in
ring subunits themselves-no
separate lid.
• ATP hydrolysis triggers the
closing of the lid portion.
• TriC in mammals.
13avs

14. Structure of
GroEL/GroES
system
14avs

15. • Chaperonin in protein folding- 15avs

16. 16avs

17. REFERENCES
• Text Book Of Molecular Cell Biology ,7th
Edition,by Arnold Berk, Harvey Lodish
Et.Al.,Macmillan.
• Lehninger Principles Of Biochemistry ,5th
Edition,Michael M.Cox And David L.Nelson.
• Textbook Of Biochemistry,4th
Edition,U.Sathyanarayana And U.Chakrapani.
• Hsp 70 Chaperones:cellular Functions And
Molecular Mechanism,M.P.Mayer And B.Bukau
17avs

18. Thank you…
18avs