Hop as an adaptor in the heat shock protein 70 (Hsp70) and hsp90 chaperone machinery.
Hop, an abundant and conserved protein of unresolved function, binds concomitantly with heat shock protein 70 (Hsp70) and Hsp90, participates with heat shock proteins at an intermediate stage of progesterone receptor assembly, and is required for efficient assembly of mature receptor complexes in vitro. A largely untested hypothesis is that Hop functions as an adaptor that targets Hsp90- to Hsp70-substrate complexes; if true, then loss of either Hsp70 binding or Hsp90 binding by Hop should equally disrupt its ability to promote assembly of mature receptor complexes. To generate Hop mutants that selectively disrupt heat shock protein interactions, highly conserved amino acids in the previously mapped Hsp70 and Hsp90 binding domains of Hop and in a conserved C-terminal domain were targeted for small substitutions and deletions. In co-precipitation assays, these mutants displayed selective loss of association with heat shock proteins. In assays using Hop-depleted rabbit reticulocyte lysate for the cell-free assembly of receptor complexes, none of the Hop mutants inhibited Hsp70 binding to receptor, but all mutants were defective in supporting Hsp90-receptor interactions. Thus, Hop has a novel role in the chaperone machinery as an adaptor that can integrate Hsp70 and Hsp90 interactions.
Chen
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Department of Pharmacology, University of Nebraska Medical Center, Omaha, Nebraska 68198-6260, USA.
Smith
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DF
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D017124:Conserved Sequence; D029721:Drosophila Proteins; D005057:Eukaryotic Cells; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D053612:Janus Kinases; D008954:Models, Biological; D018832:Molecular Chaperones / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011817:Rabbits; D011980:Receptors, Progesterone; D020449:Repetitive Sequences, Amino Acid; D012156:Reticulocytes; D014157:Transcription Factors
D029721:Drosophila Proteins; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D018832:Molecular Chaperones; D011980:Receptors, Progesterone; D014157:Transcription Factors; D011505:Protein-Tyrosine Kinases; D053612:Janus Kinases; C085845:hop protein, Drosophila