BAG-1, a negative regulator of Hsp70 chaperone activity, uncouples nucleotide hydrolysis from substrate release

David Bimston, Jaewhan Song, David Winchester, Shinichi Takayama, John C. Reed, Richard I. Morimoto*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

149 Scopus citations


Molecular chaperones influence the process of protein folding and, under conditions of stress, recognize non-native proteins to ensure that misfolded proteins neither appear nor accumulate. BAG-1, identified as an Hsp70 associated protein, was shown to have the unique properties of a negative regulator of Hsp70. Here, we demonstrate that BAG-1 inhibits the in vitro protein refolding activity of Hsp70 by forming stable ternary complexes with non-native substrates that do not release even in the presence of nucleotide and the co-chaperone, Hdj-1. However, the substrate in the BAG-1-containing ternary complex does not aggregate and remains in a soluble intermediate folded state, indistinguishable from the refolding-competent substrate-Hsp70 complex. BAG-1 neither inhibits the Hsp70 ATPase, nor has the properties of a nucleotide exchange factor; instead, it stimulates ATPase activity, similar to that observed for Hdj-1, but with opposite consequences. In the presence of BAG-1, the conformation of Hsp70 is altered such that the substrate binding domain becomes less accessible to protease digestion, even in the presence of nucleotide and Hdj-1. These results suggest a mechanistic basis for BAG-1 as a negative regulator of the Hsp70-Hdj-1 chaperone cycle.

Original languageEnglish (US)
Pages (from-to)6871-6878
Number of pages8
JournalEMBO Journal
Issue number23
StatePublished - Dec 1 1998


  • BAG-1
  • Hsp70
  • Protein folding
  • Substrate release
  • Ternary complex

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Biochemistry, Genetics and Molecular Biology(all)
  • Immunology and Microbiology(all)


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