Molecular chaperones are proteins that assist in the folding of other proteins but are not part of the final folded structure. They help prevent misfolding and aggregation of proteins. The first observations of molecular chaperones date back to the 1970s but their function was not fully understood until the 1980s and 1990s when it was discovered that they play a key role in protein folding and homeostasis. Molecular chaperones are found in all compartments of the cell where protein folding occurs and help protect proteins from misfolding, especially under stressful conditions.

1. BS. Biotechnology
Instructor
Miss Mahwish Batool Kazmi
Submitted By:
Muhammad Junaid (BsBt-13-f-10)
Muhammad Anas (BsBt-13-f-41)
Rizwan Abbas (BsBt-13-f-43)
BAHAUDDIN ZAKARIYA UNIVERSITY LAHORE CAMPUS
All about molecular chaperones
Assignment of Biochemistry
ABSTRACT;
This is our group assignment on topic Molecular chaperones submitted to Madam Mahwish
Kazmi. All of us participated in collection of the data and prepared it.
The references are also given with the table of contents

2. 1
All about molecular chaperones
Content and references
S.no Tittle Reference Page
A
Introduction.
Explanation.
History.
F-U. Hartl, Molecular chaperones in
cellular protein folding, Nature 381
(1996), 571–580.
02
B
Structure of molecular
chaperones.
Location ?
General microbiology
Book by g.tortora and funke –case
www.biomed.com /articles
04
C
Properties of Chaperones.
Significance of Chaperon.es
A text book Of cytology
The world of cell by Bruce albert.5th
edition
07
D
Classification.
Types.
www.dailymotion .com videos/ali-
libra.Chemistry/Chaperonins
www.biomed.com /articles
09
E
Mechanism of action.
Example.
A text book Of cytology
The world of cell by Bruce albert.5th
edition
12
F
Uses and benefits General microbiology
Book by g.tortora and funke –case
16

3. 2
Molecular chaperones
An introduction
Chaperones can be defined as proteins which monitor non-native conformations, stabilize
proteins and assist folding processes, but are not part of the final native structures .They optimize
the folding efficiency or even facilitate folding of non-native intermediates that would otherwise
be kinetically trapped, but they do not add structural information to the folding process
Chaperonins
Chaperonins are proteins Protein folding is assisted by a group of proteins known as molecular
chaperones that provide favourable conditions for the correct folding of other proteins, thus
preventing aggregation. Newly made proteins usually must fold from a linear chain of amino
acids into a three-dimensional form.
Chaperonins belong to a large class of molecules that assist protein folding, called molecular
chaperones. The energy to fold proteins is supplied by adenosine triphosphate (ATP)..
Other Definition
According to Ellis, 1993:
“Molecular chaperones are defined as a functional class of unrelated families of proteins that
assist the correct non-covalent assembly of other polypeptide containing structures in vivo, but
are not components of these assembled structures when they are performing their normal
biological functions.”
Anfinsen in 1973 said that
“Molecular chaperones are the guardians of protein homeostasis. Proteins require a particular
three dimensional structure in order to fulfil their function, despite being synthesised as a linear
string of amino acids joined by peptide bonds.”
According Mayer view 2010
Molecular chaperones are catalysts in the physiological folding process, which, through
transient non-covalent associations with proteins, prevent aggregation and misfolding during de
novo folding as well as regulating subsequent stages of protein translocation and complex
formation.

4. 3
Explanation
The term molecular chaperone is used to describe a functionally related set of proteins.
According to their molecular weight, molecular chaperones are divided into several classes or
families. A cell may express multiple members of the same chaperone family. For example, the
yeast S. cerevisiae produces 14 different versions of the chaperone Hsp70.
Proteins from the same class of molecular chaperones often show a significant amount of
sequence homology and are structurally and functionally related, whereas there are hardly any
homologies between chaperones from different families. Despite this diversity, however, most
molecular chaperones share common functional features
These amino acids must subsequently fold to achieve the appropriate spatial arrangement of
these residues in order to arrive at the final three dimensional structure of the protein. Sequence
determines structure; the information required to adopt a native three-dimensional conformation
is encoded in the primary amino acid sequence, although the number of possible theoretical
conformations of even a small protein is tremendously large under non-physiological or stressful
conditions.
Protein molecules are responsible for almost all biological functions in cells. In order to fulfil
their various biological roles, these chain-like molecules must fold into precise three-dimensional
shapes. Incorrect folding and clumping together of proteins is being recognized as the cause for a
growing number of age-related diseases, including Alzheimer’s and Parkinson’s disease as well
as other neurodegenerative disorders.
Most biological functions in living cells are performed by proteins, chain-polymers of amino
acids that are synthesized on ribosomes based on genetic information.
Upon synthesis, protein chains must fold into unique three-dimensional structures in order to
become biologically active. While in the test-tube this folding process can occur spontaneously,
in the cell most proteins require assistance for proper folding by so-called ‘molecular
chaperones’.
These are specialized proteins which protect other, not-yet folded proteins from miss folding
and clumping together (aggregating) in the highly crowded cellular environment. However,
proteins do not always fold correctly, despite the existence of a complex cellular machinery of
protein quality control.
In particular, an increasing number of neurodegenerative diseases have been recognized in
recent years to be caused by the accumulation of protein aggregates in the brain and other parts
of the central nervous system.

5. 4
Where are the molecular chaperones located?
Molecular chaperones are found in all compartments of a cell where folding or, more generally,
conformational rearrangements of proteins occur. Although protein synthesis is the major source
of unfolded polypeptide chains, other processes can generate unfolded proteins as well. At non
physiological high temperatures or in the presence of certain chemicals, proteins can become
structurally labile and may even unfold.
Eventually, this would result in loss of function of the affected proteins and in the accumulation
of protein aggregates. The cell responds to this threat by producing increasing amounts of
specific protective proteins, a phenomenon referred to as heat-shock response or stress .Many of
these proteins were found to be molecular chaperones.
 It is not necessarily that all molecular chaperone families are present in the three domains
of life; some are highly specialized and are found in just one domain
 Eukaryotes have evolved not only more different families of chaperones, but typically
have more members (e.g., Hsp70, small Hsps, prefoldin, etc.)
 related to diversity of processes? (eukaryotes have organelles, greater diversity of cell
functions)
 In bacteria, the archetype is the well-characterized chaperonin GroEL from E. coli.
 In archaea, the chaperonin is called the thermosome.
 In eukarya, the chaperonin is called CCT (also called TRiC or c-cpn).
 These protein complexes appear to be essential for life in E. coli, Saccharomyces
cerevisiae and higher eukaryotes. While there are differences between eukaryotic,
bacterial and archaeal chaperonins, the general structure and mechanism are conserved.
Normal protein folding carried by direction of DNA in cytosol

6. 5
History of chaperones
The first use of the notion of chaperones was for a toxin present in the venom of the Australian
taipan snake (Fohlman et al 1976). The two protein subunits surrounding the active neurotoxic
subunit were described as chaperones that increase the specificity of the toxin and protect it
against degradation. No extension of the notion of chaperone to other systems was then
attempted.
The same is true for Ron Laskey’s famous discovery of the chaperone action of nucleo plasmin
on histones, allowing their correct assembly into nucleosomes. The role of nucleo plasmin is
transient: it is not part of the full nucleosome assembly. Its sole function is to prevent premature,
improper interactions between positively charged histones and the negatively charged DNA
molecule. The requirement for nucleo plasmin is not absolute, and can be lifted by a very slow in
vitro decrease in ionic strength during nucleosome assembly.
The history of the discovery of the chaperones was rich and tortuous. Chaperone function was
the last of the main cellular functions to emerge from . . . nothing: both the central dogma of
molecular biology and the experiments of Christian Anfinsen supported the hypothesis that the
folding of proteins and their assembly into macromolecular complexes were spontaneous
processes, requiring no assistance.
It was through the study of the heat shock response that the generality of chaperone function
emerged. There is a long tradition of research into the effects of heat on organisms, including the
possibility of mimicking genetic mutations by phenocopies. The modern history of the cellular
heat shock response started with the observation by Ferruccio Ritossa in 1962 that a transient
increase in temperature activates the expression of a small group of Drosophila genes (Ritossa
1962, 1996).
From the end of the 1970s to the discovery of chaperone function, many observations obscured
rather than clarified the picture: overexpression of these proteins in cancer, association of some
of them with oncogenic protein kinases as well as steroid hormone receptors, high expression at
specific steps of differentiation and development. Hypotheses concerning the role of these
proteins in metabolism, or in the control of cytoskeletal structure, were proposed before Hugh
Pelham opened the way to chaperone function with his 1985observations.
In 1986, he generalized the picture by including what was known of the behaviour of BiP, a
protein interacting with many proteins transiting through the reticulum before their assembly into
macromolecular complexes: he demonstrated that BiP was also a member of the HSP70 family
(Munro and Pelham 1986; Pelham 1986).
John Ellis who named the function in 1987 from his observations of a very different
experimental system, the assembly of ribulose 1–5 diphosphate carboxylase (Rubisco) – the
enzyme responsible for assimilation of CO2 in chloroplasts (Ellis 1996).

7. 6
A Rubisco-binding protein was discovered in 1980, and its chaperoning of Rubisco progressively
demonstrated. The credit of that protein folding is not assisted is rather recent in the history of
molecular biology, the consequence of the main hypotheses proposed by Francis Crick in 1957,
and of the experiments performed by Christian Anfinsen at the beginning of the 1960s. Before
then, the dominant idea was that proteins were ‘moulded’ on protein-forming centres.
The dogma is not violated since chaperones do not orient the folding process but only prevent
parasitic reactions such as protein aggregation. The hypothesis that chaperones could have an
active role, a steric action on their protein targets, was not totally rejected by John Ellis –
although it is hard to reconcile with the general action of chaperones – and still haunts the
dreams of many biologists. It has been proposed that the highly specific characteristics of prions
might be explained by a self-chaperoning activity of these proteins (Liautard 1991).
Structure of molecular chaperones
Most of the cellular processes are executed by sets of proteins that work like molecular machines
in a coordinated manner, thus acting like an assembly line and making the process a more
efficient one. One of such assembly lines is the one formed by molecular chaperones, a group of
proteins involved in cell homeostasis through two opposite functions, protein folding and
degradation. Over the last years it has been found that chaperones are not only devoted to
assisting the folding of other proteins, but also given the right conditions and the presence, they
can be active players in protein degradation. The two processes are carried out through the
transient formation of complexes between different chaperones and co-chaperones. Our goal is
the structural characterization of some of these complexes, using as a main tool electron
microscopy and image processing techniques, and combining the information obtained with the
available atomic structures of some of these chaperones and co-chaperones, with the aim of
understanding the structural mechanisms by which these complexes function. Another objective
is to characterize, for some of these chaperones, the forces involved in their activity, using the
novel technique of optical tweezers.
Structural view of eukaryotic Chaperone

8. 7
Properties of Chaperones
Molecular chaperones can be broadly defined as proteins which interact with non-native states of
other protein molecules.
This activity is important in the folding of newly synthesized polypeptides and the assembly of
multi subunit structures; the maintenance of proteins in unfolded states suitable for translocation
across membranes; and the stabilization of inactive forms of proteins which are turned on by
cellular signals; and the stabilization of proteins unfolded during cellular stress.
The major chaperone classes are hsp60 (including TCP1), hsp70 and hsp90 Molecular
chaperones:
All these proteins prevent the aggregation of unfolded proteins and the strength of interaction
with their protein substrates is modified by the binding and hydrolysis of ATP. Hsp70 is a di
meric and ubiquitous protein which binds its substrates in an extended conformation through
hydrophobic interactions. It binds to newly synthesized proteins and is required for protein
transport.
In its ATP-bound state it has a low protein affinity but when the nucleotide is hydrolysed to give
the ADP state the affinity is increased. Hsp70 in E. coli (Dna K) is regulated by two co-proteins:
Dna-J (of which there are homologues in eukaryotes) stimulates hydrolysis of ATP and Grp E
promotes the dissociation of ADP to allow rebinding of ATP. Thus Dna-J promotes the
association of substrate proteins and Grp-E promotes dissociation.
Hsp60 is a large, tetra deca-meric protein with a central cavity in which non-native protein
structures are proposed to bind. It is essential for the folding of a huge spectrum of unrelated
proteins and is present in all biological compartments except the ER. As in hsp70, the binding of
ATP stimulates release of the substrate and its hydrolysis restores high binding affinity.
It functions in conjunction with a co-protein, cpn10, which enhances its ability to eject proteins
during the ATPase cycle.
The enhancement of folding yields arises either from the prevention of irreversible aggregation
or the ability to unfold misfolded structures and allow further attempts to arrive at the native
state. Proteins of the hsp90 class are found associated with inactive or unstable substrate proteins
within the cell, thus preventing their aggregation and/or permitting rapid activation.
Steps
 Switch side of ATP binding each time.
 Switch side of GroES binding for each folding rxn
 Switch side of protein docking for each folding rxn

9. 8
Significance of molecular Chaperones
 Molecular chaperones, including the extracellular protein clusterin (CLU), play a
significant role in maintaining Proteo stasis they have a unique capacity to bind and
stabilize non-native protein conformations, prevent aggregation, and keep proteins in a
soluble folding competent state.
 Molecular chaperones play a prominent role in signalling and transcriptional regulatory
networks of the cell. Recent advances uncovered that chaperones act as genetic buffers
stabilizing the phenotype of various cells and organisms and may serve as potential
regulators of a system.
 Chaperones have weak links, connect hubs, are in the overlaps of network modules and
may uncouple these modules during stress, which gives an additional protection for the
cell at the network-level.
 Moreover, after stress chaperones are essential to re-build inter-modular contacts by their
low affinity sampling of the potential interaction partners in different modules.
 Most of the molecular interactions of our cells, like the self association of lipids to
membranes, are rather unspecific and can be described in general terms. However, a
relatively restricted number of interactions between cellular molecules have a high
affinity, are unique and specific, and require a network approach for a better
understanding and prediction of their changes after various environmental changes, like
stress.
 Molecular chaperones bind and release a large number of damaged proteins, which
requires a large promiscuity in their interactions. Not surprisingly, chaperones form low
affinity, dynamic temporary interactions (weak links) in cellular networks.
Processing of Chaperone action

10. 9
 Cellular stress could include a wide range of stimuli, including heat, oxidation and
chemicals. The main biological consequence of cellular stress is the loss of protein
function due to stress induced protein unfolding and aggregation. This loss is potentially
disastrous for any cell that cannot overcome it.
 Molecular chaperones prevent aggregation and promote refolding after stress and hence
promote cell survival. This so-called stress response is ubiquitous and conserved across
all organisms.Chaperone assisted protein folding in cells islargely controlled by a group
of proteins known as heat shock proteins (HSP)
 The chaperones existing in Cellular networks are remodelled in various diseases and after
stress. Proper interventions to push the equilibrium towards the original state may not be
limited to single target drugs, which have a well-designed, high affinity interaction with
one of the cellular proteins.
 Chaperones protect our cells—chaperones are good. Not always. When chaperones
protect our malignant cells—they are not really beneficial.One major from function of
chaperones is to prevent both newly synthesised polypeptide chains and assembled
subunits aggregating into non-functional structures.
 It is for this reason that many chaperones, but by no means all, are also heat shock
proteins because the tendency to aggregate increases as proteins are denatured by stress.
In this case, chaperones do not convey any additional steric information required for
proteins to fold. However, some highly specific 'steric chaperones' do convey unique
structural (steric) information onto proteins, which cannot be folded spontaneously.
Specificity of Chaperone action

11. 10
Classification of molecular chaperones
On the basis of the functioning mode in specific points molecular chaperones are categorized as
follows
Intra molecular chaperones
Intra molecular chaperones are essential for protein folding, but not required for protein function.
Considerable evidence shows that chaperones play a critical role in protein folding both in vivo
and in vitro. Unlike their molecular counterparts, intra molecular chaperones are encoded in the
primary sequence of the protein as an N-terminal or C-terminal sequence extension and are
usually termed pro peptides or pro sequences.
Upon mediation of the protein folding, the intra molecular chaperones are removed either by
auto-processing in the case of proteases or by an exogenous process in the case of non-protease
proteins.
The discovery of the first intra molecular chaperone was based on the studies on sub-tilisin, an
alkaline serine protease from bacillus sub-tilis. Often, the relation of intra molecular chaperones
to the molecular mechanism of protein folding is studied by introducing amino acid substitution
mutations in the pro peptide region but not in the functional domain of the protein.
It was shown that the addition of pro peptides in Trans allowed for the folding of the sub-tilisin
at a higher efficiency and rate than when folded in cis.
It was also shown that if the energy barrier of the transition state in sub-tilisin was reduced, it
was allowed to fold without the intra molecular chaperone, but at a slower rate.
Distinct from the sub-tilisin protease, the NGF (nerve growth factor) pro peptide forms a
cysteine knot by virtue of three intra molecular di sulfide bonds.
The pro peptide acts as a competitive inhibitor for the receptor binding of the mature NGF dimer.
It is likely that the quaternary structure may stabilize the tertiary structure.
Intra molecular chaperones are classified into two groups on the basis of their roles in protein
folding.
The type I intra molecular chaperones mediate the folding of proteins into their respective
tertiary structures and are mostly produced as the N-terminal sequence extension.
The type II intra molecular chaperones mediate the formation of the quaternary or functional
structure of proteins, and usually are located at the C-terminus of the protein.

12. 11
Type I intra molecular chaperones.
Competitive inhibition: substrate (S) and inhibitor (I) compete for the active site.
It is suggested that the α-lytic protease folds through a nucleation mechanism, in which the pro
peptide folds first and acts as a scaffold that stabilizes the C-terminal domain of the mature
protease. This allows for the structural arrangement of the two domains to pack into the native
structure. Sometimes the C-peptide has independent physiological functions. For example, the C-
peptide of pro insulin both stimulates Na+, K+-ATPase and functions as an intra-molecular
chaperone for folding of insulin.
Type II intra molecular chaperones
Intra molecular chaperones that are involved in the folding of the quaternary structure of proteins
are called type II intra molecular chaperones. The E. Coli K1-specific bacteriophages contain tail
spikes that exist as homo trimmers of endo-sialidases. These tail spikes are produced with a C-
terminal domain (CTD) that is not part of the functional trimmer. The fact that the CTD folds
independently from the enzymatic domain and forms a hexa-mer suggests that the CTD is able to
associate with each other to initiate the tri merization of endo sialidases.
There exists both an N-terminal and a C-terminal propeptide in the fibril-forming collagen. The
C-terminal propeptide prevents premature fibril formation, while the N-terminal propeptide is
important in fibril associate of the collagen triple helix. The propeptide is proteo lytically
processed in the functional multimer.
Other categories
Group I
Group I chaperonins are found in bacteria as well as organelles of endosymbiotic origin:
chloroplasts and mitochondria.The GroEL/GroES complex in E. coli is a Group I chaperonin and
the best characterized large (~ 1 MDa) chaperonin complex. GroEL is a double-ring 14mer with
a greasy hydrophobic patch at its opening and can accommodate the native folding of substrates
15-60 kDa in size.
GroES is a single-ring heptamer that binds to GroEL in the presence of ATP or transition state
analogues of ATP hydrolysis, such as ADP-AlF3. It's like a cover that covers GroEL
(box/bottle).GroEL/GroES may not be able to undo protein aggregates, but kinetically it
competes in the pathway of misfolding and aggregation, thereby preventing aggregate formation.

13. 12
Group II
Group II chaperonins, found in the eukaryotic cytosol and in archaea, are more poorly
characterized.
TRiC (TCP-1 Ring Complex, also called CCT for chaperonin containing TCP-1), the eukaryotic
chaperonin, is composed of two rings of eight different though related subunits, each thought to
be represented once per eight-membered ring. TRiC was originally thought to fold only the
cytoskeletal proteins actin and tubulin but is now known to fold dozens of substrates.
Mm cpn (Methanococcus maripaludis chaperonin), found in the archaea Methanococcus
maripaludis, is composed of sixteen identical subunits (eight per ring). It has been shown to fold
the mitochondrial protein rhodanese; however, no natural substrates have yet been identified.[3]
Group II chaperonins are not thought to utilize a GroES-type cofactor to fold their substrates.
They instead contain a "built-in" lid that closes in an ATP-dependent manner to encapsulate its
substrate.
. Chaperones in prokaryotes and eukaryotes

14. 13
Mechanism of Chaperone Action
Chaperonins undergo large conformational changes during a folding reaction as a function of the
enzymatic hydrolysis of ATP as well as binding of substrate proteins and cochaperonins, such as
GroES. These conformational changes allow the chaperonin to bind an unfolded or misfolded
protein, encapsulate that protein within one of the cavities formed by the two rings, and release
the protein back into solution. Upon release, the substrate protein will either be folded or will
require further rounds of folding, in which case it can again be bound by a chaperonin.
Step involved are
 Switch side of ATP binding each time
 Switch side of GroES binding for each folding rxn
 Switch side of protein docking for each folding rxns
The exact mechanism by which chaperonins facilitate folding of substrate proteins is unknown.
According to recent analyses by different experimental techniques, GroEL-bound substrate
proteins populate an ensemble of compact and locally expanded states that lack stable tertiary
interactions. A number of models of chaperonin action have been proposed, which generally
focus on two (not mutually exclusive) roles of chaperonin interior: passive and active.
Passive models treat the chaperonin cage as an inert form, exerting influence by reducing the
conformational space accessible to a protein substrate or preventing intermolecular interactions
e.g. by aggregation prevention.The active chaperonin role is in turn involved with specific
chaperonin–substrate interactions that may be coupled to conformational rearrangements of the
chaperonin.
Mechanism of chaperone action

15. 14
The free energy in form of ATP is used for proper functioning.
Probably the most popular model of the chaperonin active role is the iterative annealing
mechanism (IAM), which focus on the effect of iterative, and hydrophobic in nature, binding of
the protein substrate to the chaperonin.
According to computational simulation studies, the IAM leads to more productive folding by
unfolding the substrate from misfolded conformations or by prevention from protein misfolding
through changing the folding pathway.Conservation of structural and functional homology is
managed while the processing.
Molecular chaperones assist protein folding in vivo
A multitude of molecular chaperones works in protein quality control and supports protein
folding in all living organisms. Chaperones act in various cellular processes: they assist de novo
folding, refolding of stress-denatured or aggregated proteins, assembly of oligomeric proteins,
protein transport, proteolytic degradation, and, in some cases, control the activity of folded client
proteins. Depending on their respective functions, some chaperones are constitutively expressed,
whereas others are stress-induced, e.g. at higher temperatures or other conditions perturbing
protein homeostasis (hence the generic term “heat shock proteins” (Hsps) for many chaperones).
Protein folding by chaperones
FunctionisenhancedbyATP

16. 15
 A typical feature of chaperones is the stoichiometric and transient binding of non-native
polypeptides mostly at exposed hydrophobic patches.
 Chaperone binding stabilizes productive folding intermediates, hinders non-native
proteins from building incorrect intra- and intermolecular interactions and in this way
reduces protein misfolding and aggregation.
 In some instances, chaperone binding additionally triggers transient local unfolding and
Chaperones may act as “holdases” stabilizing non-native protein conformations, as
“foldases” assisting folding to the native state or as “unfoldases” unfolding misfolded
protein species or extracting proteins from aggregatesand .
 While substrate holding can be energy-independent, active assistance of productive
folding (e.g. by Hsp70 or Hsp60 chaperone systems) often requires cycles of ATP-
regulated binding and release.
 Two different groups of chaperones support folding of newly synthesized polypeptides in
all three domains of life and at first, ribosome-associated chaperones co-translationally
interact with growing polypeptide chains and guide the initial steps of de novo folding.
 After that, downstream chaperones, which do not bind to ribosomes, may further assist de
novo folding both during and after translation.
Here, we review the current knowledge on the best-characterized ribosome-associated
chaperone so far: Escherichia coli Trigger Factor.
Protein folding
Protein folding is a highly complex process by which proteins are folded into their biochemically
functional three-dimensional forms. The hydrophobic force is an important driving force behind
protein folding. The polar side chains are usually directed towards and interact with water, while
the hydrophobic core of the folded protein consists of non-polar side chains. Other forces that are
favorable for protein folding are the formation of intramolecular hydrogen bonds and van der
Waals forces.
Protein folding is entropically unfavorable because it minimizes the dispersal of energy and adds
order to the system. However, the summation of the hydrophobic effect, hydrogen bonding, and
van der Waals forces is greater in magnitude than the loss of entropy. Protein folding is therefore
a spontaneous process because the sign of ΔG (Gibbs free energy) is negative.
For a reaction at constant temperature and pressure, the change
ΔG in the Gibbs free energy is:
Delta G = Delta H - T Delta S ,

17. 16
The sign of ΔG depends on the signs of the changes in enthalpy (ΔH) and entropy (ΔS), as well
as on the absolute temperature (T, in kelvin). Notice that ΔG changes from positive to negative
(or vice versa) where T = ΔH/ΔS.
When ΔG is negative,
The process or chemical reaction proceeds spontaneously in the forward direction.
When ΔG is positive, the process proceeds spontaneously in reverse.
When ΔG is zero, the process is already in equilibrium, with no net change taking place over
time.
In molecular biology, molecular chaperones are proteins that assist the non-covalent folding or
unfolding and the assembly or disassembly of other macromolecular structures. Chaperones are
not present when the macromolecules perform their normal biological functions and have
correctly completed the processes of folding and/or assembly. The common perception that
chaperones are concerned primarily with protein folding is incorrect. The first protein to be
called a chaperone assists the assembly of nucleosomes from folded histones and DNA and such
assembly chaperones, especially in the nucleus, are concerned with the assembly of folded
subunits into oligomeric structures.
Example
The Hsp70 System
The Hsp70 proteins constitute the central part of an ubiquitous chaperone system that is present
in most compartments of eukaryotic cells, in eubacteria, and in many archaea.
Hsp70 is comprised of two functional entities: an N-terminal ATPase domain, and a smaller C-
terminal peptide-binding domain.
Hsp70 proteins are involved in a wide range of cellular processes, including protein folding and
degradation of unstable proteins The common function of Hsp70 in these processes appears to be
the binding of short hydrophobic segments in partially folded polypeptides, thereby preventing
aggregation and arresting the folding process DnaK and many other Hsp70 chaperones interact
in vivo with two classes of partner proteins that regulate critical steps of its functional cycle,
Partner Proteins of Hsp70–Modulation of the Functional Cycle
Hsp40 belongs to a diverse class of proteins that consist of multiple functional domains. One of
the domains, the amino-acid J domain, is conserved in all Hsp40 chaperones. Mutational
analysis revealed that this domain is essential forthe interaction between Hsp40 and Hsp70.[82]
Its name is derived from DnaJ, the Hsp40 protein from E. coli that cooperates with DnaK.

18. 17
The most important features of Hsp40 are that it binds to peptides, and that it stimulates
ATPhydrolysis of Hsp70.
 binding of substrate by both DnaJ and Hsc70 during transfer
 double binding could change substrate conformation
 compress substrate (confinement)
 pull apart (partial unfolding)
Benefits and uses of Chaperones
pharmacology
Molecular chaperone therapy is one of the latest pharmacological approaches to lysosomal
storage diseases. It fixes defective protein as an alternative to Stop codon suppression treatment.
These chaperones are minute molecules that can enter the central nervous system ( via Blood
Brain Barrier). Once in the CNS, they attach to the enzyme (inactive form) and fix it so that it
takes the correct functional shape.
Molecular chaperone-based vaccines offer a number of advantages for cancer treatment.
Pharmacological chaperones offer potential advantages over competing approaches to treating
genetic disorders, including oral delivery and the ability to increase enzyme activity levels in
tissues that are hard to reach, such as the central nervous system.
Functioning cycle

19. 18
Cellular fusion vaccines were made to specifically target drug-resistant cancer cells and tumour
cell populations enriched in ovarian cancer stem cells (CSC). Such vaccines showed enhanced
capacity to trigger T cell immunity to these resistant ovarian carcinoma populations.
The molecular chaperone heat-shock protein 70 (Hsp70) possesses immune stimulatory
properties that have been employed in the preparation of anticancer vaccines. Hsp70 binds
antigenic peptides in the cytoplasm of cancer cells. Hsp70 thus serves as a convenient, non-
discriminating transporter of antigens and can protect the peptides during internalization by APC
and cross presentation to T lymphocytes. We describe a method for purifying Hsp70-peptide
complexes that can be used to prepare molecular chaperone-based vaccines, involving sequential
gel filtration, ion exchange, and affinity chromatography.
Restore Protein Function
Eliminate Aggregation and/or Accumulation of Misfolded Protein
Restoring trafficking of misfolded proteins by reducing their retention in the ER has the added
potential benefit of alleviating the proteotoxic effects associated with mutant protein
accumulation and/or aggregation. Thus, our pharmacological chaperones restore protein function
and trafficking how it matters.
Protein folding and re-folding are both mediated by a highly conserved network of molecules,
called molecular chaperones and co-chaperones.
In addition to the regulatory role in protein folding, molecular chaperone function is intimately
associated with pathways of protein degradation, such as the ubiquitin-proteasome system and
the autophagy-lysosomal pathway, to effectively remove irreversibly misfolded proteins.
Chaperones are the technition of body of organisms

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The biological functions of proteins are governed by their three-dimensional fold. Proteinfolding,
maintenance of proteome integrity, and protein homeostasis (proteostasis) critically depend on a
complex network of molecular chaperones.
Disruption of proteostasis is implicated in aging and the pathogenesis of numerous degenerative
diseases. In the cytosol, different classes of molecular chaperones cooperate in evolutionarily
conserved folding pathways.
Nascent polypeptides interact cotranslationally with a first set of chaperones, including trigger
factor and the Hsp70 system, which prevent premature (mis)folding. Folding occurs upon
controlled release of newly synthesized proteins from these factors or after transfer to
downstream chaperones such as the chaperonins.
Chaperonins are large, cylindrical complexes that provide a central compartment for a single
protein chain to fold unimpaired by aggregation. This review focuses on recent advances in
understanding the mechanisms of chaperone action in promoting and regulating protein folding
and on the pathological consequences of protein misfolding and aggregation.
Conclusions
I. Chaperones are protein in nature.
II. Found mostly in all type of cells
III. They have significant role in biological world
IV. It action just like as law implications or care taker of a body.
V. Beneficial in pharmacology, therapy, and important in central dogma.
VI. It is regulator of basic process of life.
VII. They proceed voluntary as well as involuntary actions.
VIII. Help in evolutionary studies.
IX. Maintain life. Eg proteostasis is important for life.
X. Some examples are
Hsp40, Hsp70, Hsp90,GroE and substilin