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A proportion of all newly-made proteins require assistance to
convert from a linear chain of amino acids to a functional
three-dimensional entity. This process is called protein folding.
Chaperonins are protein complexes that assist the folding of
these nascent, non-native polypeptides into their native,
functional state. These proteins belong to a large class of
molecules that assist protein folding, called molecular
These molecular machines use chemical energy, in the form
of adenosine triphosphate (ATP), to promote protein folding in
all cells.
A chaperone (or occasionally chaperon) is an adult who
accompanies or supervises one or more young, unmarried
men or women during social occasions, usually with the
specific intent of preventing inappropriate social or sexual
interactions or illegal behavior (e.g., underage drinking or
illegal drug use). The chaperone is typically accountable to a
third party, usually the parents of one of the accompanied
young people.
The word derives figuratively from the French word chaperon,
meaning "hood", and later a kind of hat. This is either from this
sense or from falconry, where the same word meant the hood
placed over the head of a bird of prey to stop its desire to fly.
Traditionally, a chaperone was an older married or widowed
woman accompanying a young woman when men would be
present. Her presence was a guarantee of the virtue of the
young woman in question.
A chaperonin called GroEL-GroES
complex (from Escherichia coli)
(PDB code=1aon). Two rings of 7x2
GroEL proteins (shown in blue and
green) with a cap (just on one side)
of GroES proteins (red and yellow).
Unfolded proteins enter that cavity
(which is protein sized) to be
protected during folding
Heat shock proteins (HSP) are a class of functionally related
proteins whose expression is increased when cells are
exposed to elevated temperatures or other stress. This
increase in expression is transcriptionally regulated. The
dramatic upregulation of the heat shock proteins is a key part
of the heat shock response and is induced primarily by heat
shock factor (HSF).HSPs are found in virtually all living
organisms, from bacteria to humans.
Heat-shock proteins are named according to their molecular
weight. For example, Hsp60, Hsp70 and Hsp90 (the most
widely-studied HSPs) refer to families of heat shock proteins
on the order of 60, 70 and 90 kilodaltons in size, respectively.
Hsp90 (heat shock protein 90) is a molecular chaperone and
is one of the most abundant proteins expressed in cells. It is
a member of the heat shock protein family which is
upregulated in response to stress. Hsp90 is found in
bacteria and all branches of eukarya, but it is apparently
absent in archaea.
Heat shock protein 90 (Hsp90) is one of the most common of
the heat related proteins. The protein is named "HSP" for
obvious reasons whereas the "90" comes from the fact that it
weighs roughly 90 kiloDaltons. A 90 kDa size protein is
considered a fairly large for a non-fibrous protein.
Protein 1
Protein folding and chaperone
Hsp90 is known to associate with the non-native
structures of many proteins which has lead to the
proposal that Hsp90 is involved in protein folding
in general. Furthermore Hsp90 has been shown to
suppress the aggregation of a wide range of
"client" or "substrate" proteins and hence acts as
a general protective chaperone. However Hsp90
is somewhat more selective than other
Interaction with steroid receptors
Cancerous cells over express a number of
proteins, including growth factor receptors, such
as EGFR, or signal transduction proteins such
as PI3K and AKT (Inhibition of these proteins
may trigger apoptosis). Hsp90 stabilizes various
growth factor receptors and some signaling
molecules including PI3K and AKT proteins,
hence inhibition of Hsp90 may induce apoptosis
through inhibition of the PI3K/AKT signaling
pathway and growth factor signaling generally.
Native disorder explained
The majority of water-soluble proteins have structures that are globular and
relatively static. However, some proteins have regions that are natively
disordered. Disordered regions are flexible, dynamic and can be partially or
completely extended in solution. Native disorder also exists in global
structures such as extended random coil proteins with negligible secondary
structure or molten globules, which have regular secondary structure elements
but have not condensed into a stable globular fold. The primary function of
disorder appears to be molecular recognition of proteins and nucleic acids. It
has been speculated that the multiple metastable conformations, adopted by
disordered binding sites, allows recognition of several targets with high
specificity and low affinity. Order to disorder transitions also provide a
mechanism for controlling protein concentration via proteolytic degradation.
Disordered regions are often characterised by low sequence complexity,
compositional bias toward aromatic and hydrophilic residues and high
flexibility. The absence of a static structure means that disordered residues do
not appear in the electron density maps obtained by X-ray crystallography but
they can be investigated using other types of spectroscopy such as circular
dichroism and NMR.