The Chaperonin GroEL Switches the Reaction Cycles in Response to the Concentration of Denatured Proteins

The chaperonin GroEL is an essential molecular chaperone that mediates protein folding together with its cofactor GroES in Escherichia coli. It is widely accepted that a bullet-shaped 1 : 1 GroEL-GroES complex is formed throughout the cycle, whereas a football-shaped 1 : 2 GroEL-GroES complex is not formed. However, the accepted notion has been challenged by the recent findings that indicate the existence of the football-shaped complex. Here, we present the concept that GroEL can use both the bullet cycle and the football cycle and the choice of cycle is dependent on the concentration of denatured proteins.