Interaction of Murine BiP/GRP78 with the DnaJ Homologue MTJ1

Abstract

The activity of Hsp70 proteins is regulated by accessory proteins, among which the most studied are the members of the DnaJ-like protein family. BiP/GRP78 chaperones the translocation and maturation of secreted and membrane proteins in the endoplasmic reticulum. No DnaJ-like partner has been described so far to regulate the function of mammalian BiP/GRP78. We show here that murine BiP/GRP78 interacts with the lumenal J domain of the murine transmembrane protein MTJ1 (J-MTJ1). J-MTJ1 stimulates the ATPase activity of BiP/GRP78 at stoichiometric concentrations. The Cterminal tail of BiP/GRP78 is not required for the interaction with J-MTJ1, leaving the function of this portion of the molecule still unclear. Physical interactions between J-MTJ1 and BiP/GRP78 are stable and can be abolished by a single histidine 3 glutamine substitution in the highly conserved HPD motif shared by all DnaJlike proteins. The J-MTJ1 fragment, but not the mutant J-MTJ1:H89Q fragment, stimulates the ATPase activity of Escherichia coli DnaK, although at a higher concentration than its genuine partner DnaJ. Full-length DnaJ does not stimulate BiP over the range of concentrations investigated. These results indicate that the J domain of MTJ1 is sufficient for its interaction with BiP/GRP78 and cannot be substituted by E. coli DnaJ.

Regulation of Tissue Factor–Mediated Initiation of the Coagulation Cascade by Cell Surface Grp78

“…Our immunoprecipitation studies ( Figure 5A) support this result in that the monoclonal antibody against Grp78 (anti-Grp78 M ) coprecipitated TF, whereas anti-Grp78 G did not. The N-terminal domain of Grp78 is known to mediate ATPase activity 25 and our studies imply that this function may be independent of TF regulation because we observed no effect with antibody against the N-terminal portion of Grp78 (data not shown). Future studies involving Grp78 mutants that are deficient in ATPase activity 26 may provide further direct evidence of the functional requirements of Grp78-mediated regulation of cell surface TF-mediated initiation of the coagulation protease cascades.…”

Unfolded Protein Response-regulated Drosophila Fic (dFic) Protein Reversibly AMPylates BiP Chaperone during Endoplasmic Reticulum Homeostasis

“…The addition of the bulky AMP moiety can potentially hinder the contact between the domains and thereby disrupt the functional cycle of BiP. From an intermolecular perspective, AMPylation of BiP may also alter its interaction with binding partners such as DnaJ co-chaperone (53)(54)(55) or nucleotide exchange factors (56 -58).…”

JPDI, a Novel Endoplasmic Reticulum-resident Protein Containing Both a BiP-interacting J-domain and Thioredoxin-like Motifs

“…It has been demonstrated experimentally that Scj1 and another J-protein, Jem1, act to chaperone unfolded proteins in the yeast ER (5,15). In contrast, yeast Sec63 (16), its putative mammalian orthologue hSec63 (17), and mammalian MTJ1 (18,19), all of which are transmembrane J-proteins, seem to be directly involved in protein translocation across the ER membrane. Their similarity to bacterial DnaJ is restricted to the J-domain.…”