The protein-folding activity of chaperonins correlates with the symmetric GroEL₁₄(GroES₇)₂ heterooligomer

Chaperonins GroEL and GroES form, in the presence of ATP, two types of heterooligomers in solution: an asymmetric GroEL₁₄GroES₇ "bullet"-shaped particle and a symmetric GroEL₁₄(GroES₇)₂ "football"-shaped particle. Under limiting concentrations of ATP or GroES, excess ADP, or in the presence of 5′-adenylyl imidodiphosphate, a correlation is seen between protein folding and the amount of symmetric GroEL₁₄(GroES₇)₂ particles in a chaperonin solution, as detected by electron microscopy or by chemical crosslinking. Kinetic analysis suggests that protein folding is more efficient when carried out by a chaperonin solution populated with a majority of symmetric GroEL₁₄(GroES₇)₂ particles than by a majority of asymmetric GroEL₁₄GroES₇ particles. The symmetric heterooligomer behaves as a highly efficient intermediate of the chaperonin protein folding cycle in vitro.