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In biology, chaperones are proteins whose function is to assist other proteins in achieving proper folding. Many chaperones are heat shock proteins, that is, proteins expressed in response to elevated temperatures or other cellular stresses. The reason for this behaviour is that protein folding is severely affected by heat and, therefore, some chaperones act to repair the potential damage caused by misfolding. Other chaperones are involved in folding newly made proteins as they are extruded from the ribosome. Although most newborn proteins can fold in absence of chaperones, a minority strictly requires them. Chaperones were co-discovered by Art Horwich and Ulrich Hartl. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...
A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...
Protein folding is the process by which a protein structure assumes its functional shape or conformation. ...
Heat shock proteins (HSP) are a group of proteins the expression of which is increased when the cells are exposed to elevated temperatures. ...
Gene expression (also protein expression or often simply expression) is the process by which a genes information is converted into the structures and functions of a cell. ...
Protein folding is the process by which a protein structure assumes its functional shape or conformation. ...
More information on the various types and mechanisms of a subset of chaperones which encapsulate their folding substrates can be found in the article for chaperonins. Chaperonins are characterized by a stacked double-ring structure and are found in prokaryotes, in the cytosol of eukaryotes, and in mitochondria. Chaperonins - A proportion of all newly-made proteins require assistance to convert from a linear chain of amino acids to a functional three-dimensional entity. ...
Other types of chaperones are involved in transport across membranes, for example in the mitochondria and endoplasmic reticulum. New functions for chaperones continue to be discovered, such as assistance in protein degradation and in responding to diseases linked to protein aggregation (see prion). In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ...
The endoplasmic reticulum or ER (endoplasmic means within the cytoplasm, reticulum means little net) is an organelle found in all eukaryotic cells. ...
This article has been identified as possibly containing errors. ...
Nomenclature and examples of prokaryotic chaperones There are many different familes of chaperones; each family acts to aid protein folding in a different way. In prokaryotes like E. coli, many of these proteins are highly expressed under conditions of high stress, for example, when placed in high temperatures. For this reason, the term "heat shock protein" has historically been used to name these chaperones. The prefix "Hsp" designates that the protein is a heat shock protein. Binomial name Escherichia coli T. Escherich, 1885 Escherichia coli (usually abbreviated to E. coli) is one of the main species of bacteria that live in the lower intestines of warm-blooded animals (including birds and mammals) and are necessary for the proper digestion of food. ...
Heat shock proteins (HSP) are a group of proteins the expression of which is increased when the cells are exposed to elevated temperatures. ...
- Hsp60 (GroEL/GroES complex in E. coli) is the best characterized large (~ 1 MDa) chaperone complex. GroEL is a double-ring 14mer with a greasy hydrophobic patch at its opening; it is so large it can accommodate native folding of 54-kDa GFP in its lumen. GroES is a single-ring heptamer that binds to GroEL in the presence of ATP or ADP. GroEL/GroES may not be able to undo previous aggregation, but it does compete in the pathway of misfolding and aggregation. See (Fenton and Horwich, 2003), and the articles on GroEL/GroES for more information.
- Hsp70 (DnaK in E. coli) is prehaps the best characterized small (~ 70 kDa) chaperone. The Hsp70 proteins are aided by Hsp40 proteins (DnaJ in E. coli), which increase the ATP consumption rate and activity of the Hsp70s. It has been noted that increased expression of Hsp70 proteins in the cell results in a decreased tendency towards apoptosis. Although a precise mechanistic understanding has yet to be determined, it is known that Hsp70's have a high-affinity bound state to unfolded proteins when bound to ADP, and a low-affinity state when bound to ATP. It is thought that many Hsp70s crowd around an unfolded substrate, stabilizing it and preventing aggregation until the unfolded molecule folds properly, at which time the Hsp70s lose affinity for the molecule and diffuse away. For more information, see (Mayer and Bukau, 2005).
- Hsp90 (HtpG in E. coli) may be the least well-understood chaperone. Its molecular weight is about 90 kDa, and it is necessary for viability in eukaryotes (possibly for prokaryotes as well). Each Hsp90 has an ATP-binding domain, a middle domain, and a dimerization domain. They are thought to clamp onto their substrate protein upon binding ATP, and may require co-chaperones like Hsp70. See also (Terasawa et al, 2005).
- Hsp100 (Clp family in E. coli) proteins have been extensively studied in vivo and in vitro for their ability to target and unfold tagged and misfolded proteins. Proteins in the Hsp100/Clp family form large hexameric structures with unfoldase activity in the presence of ATP. These proteins are thought to function as chaperones by processively threading client proteins through a small 20-Å pore, thereby giving each client protein a second chance to fold. Some of these Hsp100 chaperones, like ClpA and ClpX, associate with the double-ringed tetradecameric serine protease ClpP; instead of catalyzing the refolding of client proteins, these complexes are responsible for the targeted destruction of tagged and misfolded proteins.
GroEL is a protein chaperone required for the proper folding of many proteins in prokaryotes. ...
In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ...
The initialism GFP may refer to Green fluorescent protein, a fluorescent marker frequently used in biology. ...
GroEL is a protein chaperone required for the proper folding of many proteins in prokaryotes. ...
GroEL is a protein chaperone required for the proper folding of many proteins in prokaryotes. ...
GroEL is a protein chaperone required for the proper folding of many proteins in prokaryotes. ...
Hsp70 is a family of heat shock proteins including HSP70 (also known as Hsp72), Bip and the prokaryotic protein DnaK with an approximate molecular weight of 70 kDa. ...
Apoptosis In biology, apoptosis (from the Greek words apo = from and ptosis = falling, commonly pronounced ap-a-tow-sis[1]) is one of the main types of programmed cell death (PCD). ...
The molecular chaperone Hsp90 is one of the most abundant proteins in unstressed cells. ...
Within a protein, a structural domain (domain) is an element of overall structure that is self-stabilizing and often folds independently of the rest of the protein chain. ...
Dimerization is the formation of a polymer from two similar chemical structures. ...
In biochemistry, a serine proteases or serine endopeptidases (newer name) are a class of peptidases which are characterised by the presence of a serine residue in the active center of the enzyme. ...
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