Bap (Sil1) regulates the molecular chaperone BiP by coupling release of nucleotide and substrate

  • Nat Struct Mol Biol. 2018 Jan;25(1):90-100. doi: 10.1038/s41594-017-0012-6.
Mathias Rosam  1 ,  Daniela Krader  2 ,  Christina Nickels  1 ,  Janine Hochmair  1 ,  Katrin C Back  1 ,  Ganesh Agam  2 ,  Anders Barth  2 ,  Cathleen Zeymer  3 ,  Jelle Hendrix  2  4 ,  Markus Schneider  5 ,  Iris Antes  5 ,  Jochen Reinstein  3 ,  Don C Lamb  6 ,  Johannes Buchner  7
Affiliations
  • 1. Center for Integrated Protein Science Munich at the Department of Chemistry, Technical University of Munich, Garching, Germany.
  • 2. Physical Chemistry, Department of Chemistry, Munich Center for Integrated Protein Science, Nanosystems Initiative Munich and Center for Nanoscience, Ludwig Maximilians University of Munich, Munich, Germany.
  • 3. Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany.
  • 4. Faculty of Medicine and Life Sciences and Biomedical Research Institute, Hasselt University, Hasselt, Belgium.
  • 5. Center for Integrated Protein Science Munich at the Wissenschaftszentrum Weihenstephan, Technical University of Munich, Weihenstephan, Germany.
  • 6. Physical Chemistry, Department of Chemistry, Munich Center for Integrated Protein Science, Nanosystems Initiative Munich and Center for Nanoscience, Ludwig Maximilians University of Munich, Munich, Germany. [email protected].
  • 7. Center for Integrated Protein Science Munich at the Department of Chemistry, Technical University of Munich, Garching, Germany. [email protected].
PMID: 29323281 DOI: 10.1038/s41594-017-0012-6
Abstract

BiP is the endoplasmic member of the HSP70 family. BiP is regulated by several co-chaperones including the nucleotide-exchange factor (NEF) Bap (Sil1 in yeast). Bap is a two-domain protein. The interaction of the Bap C-terminal domain with the BiP ATPase domain is sufficient for its weak NEF activity. However, stimulation of the BiP ATPase activity requires full-length Bap, suggesting a complex interplay of these two factors. Here, single-molecule FRET experiments with mammalian proteins reveal that Bap affects the conformation of both BiP domains, including the lid subdomain, which is important for substrate binding. The largely unstructured Bap N-terminal domain promotes the substrate release from BiP. Thus, Bap is a conformational regulator affecting both nucleotide and substrate interactions. The preferential interaction with BiP in its ADP state places Bap at a late stage of the chaperone cycle, in which it coordinates release of substrate and ADP, thereby resetting BiP for ATP and substrate binding.

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