CORRELATION BETWEEN THE STABILITY OF THE GROEL-PROTEIN LIGAND COMPLEXAND THE RELEASE MECHANISM

The protein-protein interactions during GroE-mediated protein refoldin g are of crucial importance for understanding how the assisted refoldi ng of non-native proteins is achieved. Since GroEL seems to be a rathe r promiscuous polypeptide-binding protein it is not surprising that co nditions for efficient dissociation fi om GroEL are promiscuous as wel l. To understand assisted protein refolding it is necessary of elucida te the underlying principles of the different partial steps of the fun ctional cycle. Here we show a correlation between the overall stabilit y of the complex between GroEL and ligand protein and the conditions f or functional release from the chaperonin. As a model system, differen tly denatured species of an antibody Fab fragment were used. While wea kly bound Fab fragments are functionally released in the absence of Gr oES, stably associated nonnative forms of the same protein are depende nt on the presence of the co-chaperonin for optimal GroE-mediated reac tivation, suggesting that complex stability determines the release req uirement. However, the observed overall stability of the complex betwe en GroEL and substrate protein may be regarded as the net product of c onstant binding and rebinding of the ligand protein, once associated w ith GroEL, as shown by competition experiments.