Review: a structural view of the GroE chaperone cycle

The GroE chaperone system consists of two ring-shaped oligomeric components whose association creates different functional states. The most remarkable property of the GroE system is the ability to fold proteins under conditions where spontaneous folding cannot occur. To achieve this, a fully functional system consisting of GroEL, the cochaperone GroES, and ATP is necessary. Driven by ATP binding and hydrolysis, this system cycles through different conformational stages, which allow binding, folding, and release of substrate proteins. Some aspects of the ATP-driven reaction cycle are still under debate. One of these open questions is the importance of so-called "football" complexes consisting of GroEL and two bound GroES rings. Here, we summarize the evidence for the functional relevance of these complexes and their involvement in the efficient folding of substrate proteins.