Dissociation of the GroEL-GroES asymmetric complex is accelerated by increased cooperativity in ATP binding to the GroEL ring distal to GroES.

A kinetic analysis of the ATP-dependent dissociation of wild-type GroEL and mutants from immobilized GroES was carried out using surface plasmon resonance. Excellent fits of the data were obtained using a double-exponential equation with a linear drift. Both the fast and slow observed dissociation rate constants are found to have a sigmoidal dependence on the concentration of ATP. The values of the Hill coefficients corresponding to the fast and slow observed rate constants of dissociation of wild-type GroEL and the Arg197-->Ala mutant are in good agreement with the respective values of the Hill coefficients previously determined for these proteins from plots of initial rates of ATP hydrolysis as a function of ATP concentration, in the presence of GroES. Our results are consistent with a kinetic mechanism for dissociation of the GroEL-GroES complex according to which GroES release takes place after an ATP-induced conformational change in the trans ring that is preceded by ATP hydrolysis and a subsequent conformational change in the cis ring. It is shown that the rate of complex dissociation increases with increasing positive cooperativity in ATP binding by the GroEL ring distal to GroES in the GroEL-GroES complex.