HEDJ, an Hsp40 co-chaperone localized to the endoplasmic reticulum of human cells.
Hsp40 co-chaperones, characterized by the presence of a highly conserved J domain, are involved in nearly all aspects of protein synthesis, folding, and secretion. Within the lumen of the endoplasmic reticulum, these chaperones are also involved in reverse translocation and degradation of misfolded proteins. We describe here the cloning and characterization of a novel Hsp40 chaperone, which we named HEDJ. Epitope-tagged HEDJ was demonstrated by confocal microscopy to be localized to the endoplasmic reticulum. Protease susceptibility, glycosidase treatment, and detergent solubility assays demonstrated that the molecule was luminally oriented and membrane-associated. In vitro experiments demonstrated that the J domain interacted with the endoplasmic reticulum-associated Hsp70, Bip, in an ATP-dependent manner and was capable of stimulating its ATPase activity. HEDJ mRNA expression was detected in all human tissues examined. Highly homologous sequences were found in mouse, Drosophila, and Caenorhabditis elegans data bases. These results suggest potential roles for HEDJ in protein import, folding, or translocation within the endoplasmic reticulum.
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Departments of Pediatrics and Molecular Microbiology, Washington University School of Medicine and St. Louis Children's Hospital, St. Louis, Missouri 63110, USA.
Haslam
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D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017173:Caenorhabditis elegans / Q000235:genetics; D002522:Chlorocebus aethiops; D004330:Drosophila / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D004926:Escherichia coli / Q000235:genetics; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000032:analysis; D006360:Heat-Shock Proteins / Q000032:analysis* / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D051379:Mice; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014709:Vero Cells
C494647:DNAJB1 protein, human; C494648:DNAJB11 protein, human; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D000251:Adenosine Triphosphatases