title: Hsc70/Hsp40 chaperone system mediates the Hsp90-dependent refolding of firefly luciferase.
abstract: BACKGROUND
  The 90-kDa heat shock protein, Hsp90, was previously shown to capture firefly luciferase during thermal inactivation, thereby preventing its irreversible off-pathway aggregation and maintaining it in a folding-competent state. However, subsequent refolding of the luciferase required addition of rabbit reticulocyte lysate.
  
  
  RESULTS
  Here we demonstrate that Hsc70 (cytosolic Hsp70) and Hsp40/Hdj1 (cytosolic DnaJ homologue) are the effective components in a reticulocyte lysate, while other unidentified factor in the lysate is also required for the refolding of Hsp90-captured luciferase. Though another cytosolic DnaJ homologue, Hdj2/HSDJ, was more efficient than Hsp40 in suppressing the aggregation of rhodanese, Hdj2 was less effective for the refolding of luciferase than Hsp40. In the absence of the third factor, Hsp40 could bind to the luciferase captured by Hsp90, which suggested that Hsp40 on its own was able to bind the substrate protein, but Hsc70 could not.
  
  
  CONCLUSIONS
  Hsc70, Hsp40 and at least another additional component in the reticulocyte lysate are necessary for full accomplishment of the refolding of Hsp90-captured luciferase. The third factor may be required for the loading of Hsc70 on to the substrate protein bound to Hsp90.
authors.affiliation: Department of Biochemistry, Oita Medical University, 1-1 Idaigaoka, Hasama-machi, Oita 879-5593, Japan. minami@oita-med.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Minami
authors.forename: M
authors.initials: M
authors.lastname: Minami
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002474:Cell-Free System; D001517:Coleoptera / Q000201:enzymology; D050883:HSC70 Heat-Shock Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism*; D019476:Insect Proteins / Q000378:metabolism; D007700:Kinetics; D008156:Luciferases / Q000737:chemistry* / Q000378:metabolism*; D011489:Protein Denaturation; D017510:Protein Folding; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D013552:Swine; D013884:Thiosulfate Sulfurtransferase / Q000737:chemistry / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D050883:HSC70 Heat-Shock Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D019476:Insect Proteins; D008156:Luciferases; D013884:Thiosulfate Sulfurtransferase