Interaction of murine BiP/GRP78 with the DnaJ homologue MTJ1.

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 C-terminal 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 --> glutamine substitution in the highly conserved HPD motif shared by all DnaJ-like 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.
Mesh Terms:
Adenosine Triphosphatases, Amino Acid Motifs, Amino Acid Sequence, Animals, Carrier Proteins, Cell Nucleus, Circular Dichroism, Dose-Response Relationship, Drug, Enzyme Activation, Escherichia coli Proteins, HSP40 Heat-Shock Proteins, HSP70 Heat-Shock Proteins, Heat-Shock Proteins, Kinetics, Mice, Microsomes, Models, Biological, Molecular Chaperones, Molecular Sequence Data, Mutagenesis, Site-Directed, Neoplasm Proteins, Peptides, Plasmids, Protein Binding, Recombinant Proteins
J. Biol. Chem.
Date: Jun. 30, 2000
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