The human cytosolic molecular chaperones hsp 9 O , hsp 7 O ( hsc 7 O ) and hdj - 1 have distinct roles in recognition of a non - native protein and protein refolding Brian

The properties of molecular chaperones in protein-assisted refolding were examined in vitro using recom-binant human cytosolic chaperones hsp9O, hsc7O, hsp7O and hdj-1, and unfolded 3-galactosidase as the sub-strate. In the presence of hsp7O (hsc7O), hdj-1 and either ATP or ADP, denatured 3-galactosidase refolds and forms enzymatically active tetramers. Interactions between hsp9O and non-native J-galactosidase neither lead to refolding nor stimulate hsp7O-and hdj-1-dependent refolding. However, hsp9O in the absence of nucleotide can maintain the non-native substrate in a 'folding-competent' state which, upon addition of hsp7O, hdj-1 and nucleotide, leads to refolding. The refolding activity of hsp7O and hdj-1 is effective across a broad range of temperatures from 22°C to 41°C, yet at extremely low (4°C) or high (>41'C) temperatures refolding activity is reversibly inhibited. These results reveal two distinct features of chaperone activity in which a non-native substrate can be either maintained in a stable folding-competent state or refolded directly to the native state; first, that the refolding activity itself is temperature sensitive and second, that hsp9O, hsp7O (hsc7O) and hdj-1 each have distinct roles in these processes.