Chaperone (protein)

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Chaperone (Engl. Chaperones ) are proteins that newly synthesized proteins in folding support. The name was chosen after the English term for chaperones , "because they protect immature proteins from harmful contact".


Newly synthesized proteins must first find their specific, native, functional conformation. This is basically in the primary structure , and smaller proteins can spontaneously fold in the right way. The classic example of spontaneous folding is the ribonuclease . In the case of larger, more complex proteins, however, tools are often necessary for correct folding, since such proteins tend to form undesirable, non-functional aggregations.

Cells have found a way to minimize the aggregation of newly synthesized proteins from the start. To do this, the cell uses a complex, highly conserved protein machinery, the chaperones. These proteins interact specifically with proteins prone to aggregation and thus compete directly with aggregation reactions. The chaperones accelerate the correct folding and association of the proteins without becoming part of the structure themselves. Only non-covalent interactions are affected. The following scheme roughly describes the function of the chaperones, where U represents the newly synthesized, still unfolded protein, which is present in a random coil structure. One way now leads to the aggregation of the protein (A), the other way through the mediation of the chaperone to the native protein N:

By far the best-studied chaperone mechanism, that of the Hsp60 group (GroEL in bacteria), is described figuratively as a hydrophobic donut hole : The chaperone resembles a "barrel" or " donut " with lids on both sides. On the inside of the barrel there are hydrophobic chains that interact with the hydrophobic areas of the unfolded protein inside and thus prevent it from undesired aggregation. As soon as the protein has reached its native conformation, the hydrophobic areas in the protein itself are saturated. Under ATP -consumption of the "lid" is opened and released the finished product from the "barrel" or "donut".

Chaperones are not only so important because they give newly synthesized proteins their functional structure, but also have an even wider meaning: Since proteins only pass through the tunnel proteins of the cell membranes (e.g. into a mitochondrion ) as long amino acid chains without any hydrogen and disulfide bonds after crossing the cell membrane, they have to be folded back so that they can regain their function. This is also the task of the chaperones.

Classification of chaperones

Chaperones are required in order to even help new amino acid chains to achieve their physiological secondary structure . The bacterial chaperone GroEL, for example, helps an estimated half of all medium-sized (30–60 kDa), newly synthesized bacterial proteins to fold. The enormous consumption of ATP , i.e. energy, that this entails underlines the importance of this process.

Many chaperones show an increased synthesis rate at unphysiologically high temperatures and thus belong to the classic heat shock proteins . However, other factors such as oxidative stress or cell-damaging substances can also lead to an accumulation of protein aggregates and thus trigger the occurrence of heat shock proteins. As early as 1988 it could be proven that there is a clear correlation between the expression of heat shock proteins and the occurrence of thermal tolerance or the ability to tolerate stressful situations to a certain extent. Sequence homologies and their molecular mass play a decisive role in the classification of heat shock proteins . With the help of these criteria, five universal classes of heat shock proteins could be distinguished:

The chaperones cannot be traced back to a common original protein. They represent a heterogeneous class, the members of which arose at different times in evolution.

Furthermore, lectin chaperones are known, to which calreticulin and calnexin belong. These help in the folding of glycoproteins .

Folding helper enzymes, such as peptidyl prolyl cis / trans isomerase or protein disulfide isomerase, are to be distinguished from chaperones .

See also


  • J. Buchner: Introduction: the cellular protein folding machinery. Cell Mol. Life Sci 59. 2002, 1587-1588.
  • H. Wegele; L. Muller; J. Buchner: Hsp70 and Hsp90 - a relay team for protein folding. Rev Physiol. Biochem. Pharmacol. 151. 2004, 1-44 (Springer Verlag).
  • Michael Groß: folding aid in motion . In: Chemistry in Our Time . tape 46 , no. 2 , 2012, p. 70 , doi : 10.1002 / ciuz.201290021 .
  • H. Fiedler: Chaperones. Lexicon of Medical Laboratory Diagnostics. 2019, p. 558. Springer Verlag.

Web links

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