REDOX MECHANISM FOR THE CHAPERONE ACTIVITY OF HEAT-SHOCK PROTEINS HSP-60, HSP-70 AND HSP-90 AS SUGGESTED BY HYDROPHOBIC CLUSTER-ANALYSIS - HYPOTHESIS

We have recently shown that the N-terminal ATPase fragment of hsp70 (1 -375, composed of domains I and II) as well as the subsequent domain I II (376-520) may share three-dimensional similarities with hsp60. In t his study, we propose that domain III, common to the hsp60s and hsp70s is also found in the hsp90s and adopts a beta-alpha-beta Rossmann-fol ded structure which is encountered in the NAD-binding domain of dehydr ogenases. Consequently, with the help of the domain IV (in hsp70s and hsp90s) or of hsp10/GroES (in hsp60s) and possibly that of auxilliary partners, the hsp molecules could act as ''unfoldases'' or ''reset sys tems'' by disrupting secondary structures through redox reactions on t he main polypeptidic chain with which they interact. The models built on this hypothesis may open up a new way for understanding the chapero ne functions within the folding/unfolding processes.