title: HSP40 binding is the first step in the HSP90 chaperoning pathway for the progesterone receptor.
abstract: The progesterone receptor (PR) can be isolated in its native conformation able to bind hormone, yet its ligand-binding domain rapidly loses its activity at elevated temperature. However, an in vitro chaperoning system consisting of five proteins (HSP40, HSP70, HOP, HSP90, and p23) with ATP is capable of restoring this function. The first step of this chaperoning mechanism is usually thought to be the binding of HSP70 to PR. Our findings here show that the binding of HSP40 to PR is, instead, the first step. HSP40 binding occurred rapidly and was not dependent on ATP or other proteins. The stoichiometry of HSP40 to native PR in these complexes was approximately 1:1. HSP40 bound specifically and with a high affinity to native PR (K(d) = 77 nm). The binding of HSP40 to PR was sustained and did not interact in the highly dynamic fashion that has been observed previously for HSP90 in this system. The HSP40 small middle dotPR complex could be isolated as a functional unit that could, after the addition of the other chaperones, progress to a PR complex capable of hormone binding. These results indicate that HSP40 initiates the entry of PR into the HSP90 pathway.
authors.affiliation: Department of Biochemistry and Molecular Biology, Mayo Graduate School, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: M Patricia
authors.initials: MP
authors.lastname: Hernández
authors.forename: Ahmed
authors.initials: A
authors.lastname: Chadli
authors.forename: David O
authors.initials: DO
authors.lastname: Toft
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002645:Chickens; D018076:DNA, Complementary / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; 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*; D006801:Humans; D019746:Intramolecular Oxidoreductases; D007700:Kinetics; D051379:Mice; D008956:Models, Chemical; D018832:Molecular Chaperones / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D000071876:Prostaglandin-E Synthases; D011485:Protein Binding; D017510:Protein Folding; D020033:Protein Isoforms; D011980:Receptors, Progesterone / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors
chemical_list: D018076:DNA, Complementary; 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; D010750:Phosphoproteins; D020033:Protein Isoforms; D011980:Receptors, Progesterone; C079373:STIP1 protein, human; C489791:Stip1 protein, mouse; D000255:Adenosine Triphosphate; D019746:Intramolecular Oxidoreductases; C490849:PTGES3 protein, human; D000071876:Prostaglandin-E Synthases