Chaperonien

Chaperonien, also known as chaperonins, are a family of molecular chaperones that assist in the folding of polypeptides into their native structures. They are large oligomeric complexes that create an isolated chamber in which substrate proteins can fold, preventing aggregation.

In bacteria and organelles, Group I chaperonins form two stacked rings of seven subunits (GroEL) that enclose a central cavity; GroES acts as a detachable lid.

In archaea and eukaryotes, Group II chaperonins form similar two-ring structures but do not use a separate lid; instead, a built-in flexible lid formed by the apical domains closes the chamber.

Substrate binding to the cis ring, ATP binding and hydrolysis drive conformational changes that encapsulate the substrate; after folding, the chamber opens and the folded protein is released into the cytosol.

Chaperonien are localized in bacteria and organelles; eukaryotic cytosol houses CCT (chaperonin-containing TCP-1 complex) with eight different subunits per ring; archaea contain Group II chaperonins; mitochondria and chloroplasts house Group I or specialized forms.