ATP induces non-identity of two rings in chaperonin GroEL

For its function, the Escherichia coli chaperonin GroEL requires the presence of ATP and co-chaperonin GroES. We have observed that ADP displays a two-step inhibition of GroEL-dependent ATP hydrolysis, wherein one-half of the GroEL ATPase sites is strongly inhibited by ADP while the other half is affected very mildly. It is suggested that interaction with ATP induces structural and functional differences between two initially identical rings in GroEL (inter-ring negative cooperativity) and that the subsequent binding of GroES occurs to the ring that is occupied first by ATP in a positively cooperative manner.