GroEL/GroES mechanism of action and formation of complexes during reaction cycle: a matter of debate

The bacterial chaperonin GroEL alongwith its cochaperonin GroES is the paradigmatic molecular chaperone machine for protein folding. Most bacterial proteins require the GroEL chaperonin for proper folding. This review aims to discuss the types of reaction cycles of the GroEL/ES chaperone complex depending upon the concentration of substrate proteins, ATP, and certain ions, through formation of different kinds of complexes. The molecular mechanisms behind formation of these complexes have also been highlighted. The GroEL has been found to undergo the asymmetric and symmetric cycles of protein folding depending on the presence and absence of substrate proteins through formation of different complexes which occur by any of the three mechanisms: active cage model, passive cage model, or iterative annealing model.