'Chaperones' ([šeprony], from fr. Chaperons - gardedámy) are proteins involved in the folding of other proteins. Chaperones are applied in three ways :
- "Help" proteins to pack properly (= find the spatial arrangement corresponding to the native conformation); sometimes they can even allow the protein to unfold;
- prevent proteins from curling prematurely;
- prevent intermolecular interactions of unpackaged proteins and thus their precipitation.
They are ATPases. Although they are similar to enzymes, they are not specific for their ligands. Formerly also referred to as "stress proteins" or heat shock proteins (HSPs). They were first described as proteins whose concentrations increase in Drosophila cells after exposure to high temperatures . Their synthesis occurs during cellular stress, such as changes in temperature, cold, detergents, changes in pH, ionic strength, the effects of toxic substances and perhaps some foods. Thus, by synthesizing chaperones, the cell resists the denaturing effects of stress factors. Glucose regulated proteins are chaperones in the endoplasmic reticulum ( cold shock proteins ).
Examples of chaperones:
- Ubiquitin and hsp8 - regulate the degradation of cytoplasm tic proteins; upon activation, the ATP molecule binds to the lysine residue of the protein. The protein thus ubiquitous is inserted into the cavity of a suitable proteasome, where the degradation takes place. It degrades about 30% of newly synthesized polypeptides and proteins, because the first folding creates a lot of faulty intermediates that must be destroyed to maintain homeostasis in the cells.
- Hsp32 - is a hemoxygenase enzyme that oxidizes the hem portion of hemoglobin to bilirubin. It regulates the correct concentration of NADPH in cells. Decides on antioxidant metabolic protection cells.
- Hsp28 - crystallin, regulates apoptosis and filament reorganization.
- Hsp70 - the most important large chaperone complex, the largest in eukaryotic cells; contained mainly in cytoplasm, endoplasmic reticulum and mitochondria. It helps repair poorly arranged nascent or older finished polypeptide chains.