Chaperonins

This is a type of molecular chaperones. Chaperonins participate in folding and unfolding polypeptide chains, providing them with spatial structure or eliminating this structure. ATP hydrolysis energy is necessary for the function of chaperonins. Their structure resembles a barrel-shaped cage, consisting of two parts. Each part consists of 7, 8, or 9 subunits, the number depends on the type of organism. There are two groups of chaperonins:

Group I – typical for bacteria, eukaryotic mitochondria, plant chloroplasts. Certain chaperonins of this group form complexes, for example, the GroEL/GroES complex, which folds 15–60 kDa polypeptides. This complex does not release already formed protein aggregates but stops the formation of new aggregates.

Group II – typical for eukaryotes and archaea. In eukaryotes, they are found in the cytosol, for example, TRiC, also known as CCT. It was thought that TRiC only forms the spatial structure of cell cytoskeleton proteins actin and tubulin, but it turned out that it folds many cytosolic proteins. Chaperonins act as molecular turbines that undergo conformational changes due to ATP hydrolysis. Due to the conformational changes of chaperonins, the unfolded or incorrectly folded polypeptide is captured inside the chaperonin, attached, refolded, and pushed out into the cytosol. If the folding was not completely effective, the process is repeated.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė