title: Interaction between Hsc70 and DnaJ homologues: relationship between Hsc70 polymerization and ATPase activity.
abstract: We previously found that, in the presence of ATP, DnaJ homologues catalytically induce formation of a metastable Hsc70 polymer and, similarly, the DnaJ homologue auxilin catalytically induces formation of a metastable Hsc70-clathrin basket complex. Since this suggests that the induction of metastable complexes, which form in ATP but dissociate in ADP, may be a general property of DnaJ homologues, in the present study we investigated in more detail the ability of DnaJ homologues to induce polymerization of Hsc70. This study shows that DnaJ homologues induce polymerization of Hsc70 at the same rate as they induce an initial burst of Hsc70 ATPase activity, showing that polymerization is a specific effect of DnaJ homologue binding to Hsc70. However, polymerization does not always accompany the initial burst of ATPase activity. The dependence of the rates of ATPase activity and polymerization on DnaJ homologue concentration shows that DnaJ homologues bind very weakly to Hsc70 in the presence of ATP and do not bind at all in ADP. Surprisingly, however, under certain conditions the rate of polymerization appears to be independent of Hsc70 concentration, suggesting that polymerization is a first-order reaction, perhaps occurring when two Hsc70 molecules bind to a single DnaJ molecule and then shift their binding to each other. We propose that both the polymerization of Hsc70 by DnaJ homologues and the presentation of substrate by DnaJ homologues to Hsc70 involve the bringing of substrate into proximity with Hsc70 and then independently inducing rapid ATP hydrolysis to cause formation of a metastable Hsc70-substrate complex.
authors.affiliation: Laboratory of Cell Biology, Section on Cellular Physiology, National Heart, Lung and Blood Institute, Bethesda, Maryland 20892, USA.
authors.forename: C
authors.initials: C
authors.lastname: King
authors.forename: E
authors.initials: E
authors.lastname: Eisenberg
authors.forename: L E
authors.initials: LE
authors.lastname: Greene
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D005656:Fungal Proteins / Q000378:metabolism / Q000502:physiology; D050883:HSC70 Heat-Shock Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism* / Q000502:physiology; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D006868:Hydrolysis; D008954:Models, Biological; D011108:Polymers / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D013997:Time Factors
chemical_list: D002352:Carrier Proteins; D005656:Fungal Proteins; D050883:HSC70 Heat-Shock Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D011108:Polymers; D029701:Saccharomyces cerevisiae Proteins; C070319:YDJ1 protein, S cerevisiae; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases