title: The human cytosolic molecular chaperones hsp90, hsp70 (hsc70) and hdj-1 have distinct roles in recognition of a non-native protein and protein refolding.
abstract: The properties of molecular chaperones in protein-assisted refolding were examined in vitro using recombinant human cytosolic chaperones hsp90, hsc70, hsp70 and hdj-1, and unfolded beta-galactosidase as the substrate. In the presence of hsp70 (hsc70), hdj-1 and either ATP or ADP, denatured beta-galactosidase refolds and forms enzymatically active tetramers. Interactions between hsp90 and non-native beta-galactosidase neither lead to refolding nor stimulate hsp70- and hdj-1-dependent refolding. However, hsp90 in the absence of nucleotide can maintain the non-native substrate in a 'folding-competent' state which, upon addition of hsp70, hdj-1 and nucleotide, leads to refolding. The refolding activity of hsp70 and hdj-1 is effective across a broad range of temperatures from 22 degrees C to 41 degrees C, yet at extremely low (4 degrees C) or high (>41 degrees 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 hsp90, hsp70 (hsc70) and hdj-1 each have distinct roles in these processes.
authors.affiliation: Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, IL 60208, USA.
authors.forename: B C
authors.initials: BC
authors.lastname: Freeman
authors.forename: R I
authors.initials: RI
authors.lastname: Morimoto
mesh_terms: D000227:Adenine Nucleotides / Q000502:physiology; D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D002460:Cell Line; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism / Q000502:physiology*; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006360:Heat-Shock Proteins; D006801:Humans; D018832:Molecular Chaperones / Q000378:metabolism / Q000502:physiology*; D011485:Protein Binding; D017510:Protein Folding; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D018411:Spodoptera; D013696:Temperature; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D000227:Adenine Nucleotides; C494647:DNAJB1 protein, human; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D001616:beta-Galactosidase