A thermosome is a group II
chaperonin
HSP60, also known as chaperonins (Cpn), is a family of heat shock proteins originally sorted by their 60kDa molecular mass. They prevent misfolding of proteins during stressful situations such as high heat, by assisting protein folding. HSP60 bel ...
protein complex
A protein complex or multiprotein complex is a group of two or more associated polypeptide chains. Protein complexes are distinct from multienzyme complexes, in which multiple catalytic domains are found in a single polypeptide chain.
Protein c ...
that functions in
archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
. It is the homolog of eukaryotic
CCT. This
group II chaperonin is an
ATP-dependent chaperonin that is responsible for
folding
Fold, folding or foldable may refer to:
Arts, entertainment, and media
* ''Fold'' (album), the debut release by Australian rock band Epicure
* Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot
*Abov ...
or refolding of incipient or
denatured proteins.
A thermosome has two rings, each consisting of eight
subunits, stacked together to form a cylindrical shape with a large cavity at the center.
The thermosome is also defined by its
heterooligomeric nature. The complex consists of
that alternate location within its two rings.
Being a
Group II chaperonin, the thermosome has a similar structure to
group I chaperonins. The main difference, however, lies in the existence of a helical protrusion in the thermosome which composes of a built-in lid of the hydrophilic cavity.
Not only is thermosome
ATP-dependent, but the mechanism in which thermosome shifts from open to close
conformation is also temperature-dependent. The
open conformation of the ATP-thermosome exists mainly at low temperatures.
Whereas, the
closed conformation of the thermosome occurs when heating to physiological temperature.
Similar to the
GroEL
GroEL is a protein which belongs to the chaperonin family of molecular chaperones, and is found in many bacteria. It is required for the proper folding of many proteins. To function properly, GroEL requires the lid-like cochaperonin protein com ...
chaperonins in bacteria, the thermosome shows negative cooperativity since the two rings of the thermosome show different affinities for the binding of ATP. However, unlike the GroEL system, the thermosome is less affected by the concentration of ATP. In the absence of ATP, the thermosome does not have a preference for the T-state over the R-state. There is, however, an inhibition for the loading of the second ring when ADP is bound to the first ring.
The
N-terminus and C-terminus of thermosomes are arranged in an anti-parallel fashion and their interactions form part of the intra-ring interactions. Both the N-terminus and C-terminus of the thermosome have charged residues which interact with each other to contribute to the thermal stability of the thermosome. The cpn-α and cpn-β thermosomes specifically show maximum thermal stability in the pH range of 7.0 to 8.0 because this is the range where the charged N- and C-termini residues have net charges close to zero. Under lower or high pH conditions, these residues are charged and repelled each other which negatively affect thermal stability. This shows one possible way in which pH affects the stability of the thermosome.
External links
*
References
Protein complexes
Archaea biology
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