Figure 3.

GroEL-GroES reaction cycle–rings alternate in formation of folding-active cis ternary complexes. Folding is triggered when ATP and GroES bind to the same (cis) ring as polypeptide, releasing it into the GroES-encapsulated, enlarged, and now hydrophilic cavity. This very stable complex is the longest-lived state of the chaperonin system in the presence of non-native polypeptide (63), and it is weakened and prepared for dissociation by hydrolysis in the cis ring, which allows entry of ATP and non-native polypeptide into the trans ring (30). These in turn accelerate the dissociation of the cis ligands, including polypeptide. GroES binds to the ATP/polypeptide-liganded trans ring, completing formation of a new cis complex on this ring. Thus, GroEL rings alternate back and forth as folding-active (see text for additional detail).