title: A 16-kDa protein functions as a new regulatory protein for Hsc70 molecular chaperone and is identified as a member of the Nm23/nucleoside diphosphate kinase family.
abstract: Cytoplasmic Hsc70 is a multifunctional molecular chaperone. It is hypothesized that accessory proteins are used to specify the diverse chaperone activities of Hsc70. A 16-kDa cytosolic protein (p16) co-purified with Hsc70 obtained from a fish hepatocyte cell line, PLHC-1. Hsc70 also co-immunoprecipitated with p16 from PLHC-1 cells and fish liver. p16 was identified as a member of the Nm23/nucleoside diphosphate (NDP) kinase family based on its amino acid sequence similarity, NDP kinase activity, and recognition by anti-human NDP kinase-A antibody. This antibody also co-immunoprecipitated Hsc70 and NDP kinase from human HepG2 cells. p16 monomerized Hsc70 and released Hsc70 from pigeon cytochrome c peptide (Pc) but not from FYQLALT, a peptide specifically designed for high affinity binding. Therefore, p16 may modulate Hsc70 function by maintaining Hsc70 in a monomeric state and by dissociating unfolded proteins from Hsc70 either through protein-protein interactions or by supplying ATP indirectly through phosphate transfer. p16 did not affect basal or unfolded protein-stimulated ATPase activity of bovine brain Hsc70 using in vitro assays. Interestingly, bovine liver NDP kinase did not dissociate the Hsc70.Pc complex. In addition, two nonconservative amino acid subsitutions were found near the amino terminus of p16. Therefore, p16 may be a unique Nm23/NDP kinase that functions as an accessory protein for cytosolic Hsc70 in eukaryotes.
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269-3044, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Leung
authors.forename: L E
authors.initials: LE
authors.lastname: Hightower
mesh_terms: D000251:Adenosine Triphosphatases / Q000302:isolation & purification / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002417:Cattle; D002460:Cell Line; D002846:Chromatography, Affinity; D003530:Cyprinidae; D003574:Cytochrome c Group / Q000737:chemistry; D003593:Cytoplasm / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008113:Liver Neoplasms; D046911:Macromolecular Substances; D008954:Models, Biological; D018832:Molecular Chaperones / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D020559:Monomeric GTP-Binding Proteins; D054778:NM23 Nucleoside Diphosphate Kinases; D009701:Nucleoside-Diphosphate Kinase / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D000906:Antibodies; D002352:Carrier Proteins; D003574:Cytochrome c Group; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C494371:HSPA8 protein, human; D046911:Macromolecular Substances; D018832:Molecular Chaperones; D054778:NM23 Nucleoside Diphosphate Kinases; D010446:Peptide Fragments; D014157:Transcription Factors; C517938:NME1 protein, human; D009701:Nucleoside-Diphosphate Kinase; D000251:Adenosine Triphosphatases; D020559:Monomeric GTP-Binding Proteins