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 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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adenosine Triphosphatases / metabolism
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Amino Acid Motifs
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Amino Acid Sequence
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Animals
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Carrier Proteins / chemistry
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Carrier Proteins / genetics
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Carrier Proteins / metabolism*
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Cell Nucleus / metabolism
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Circular Dichroism
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Dose-Response Relationship, Drug
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Endoplasmic Reticulum Chaperone BiP
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Enzyme Activation
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Escherichia coli Proteins*
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HSP40 Heat-Shock Proteins
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HSP70 Heat-Shock Proteins / metabolism
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Heat-Shock Proteins / chemistry*
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Heat-Shock Proteins / genetics
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Heat-Shock Proteins / metabolism*
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Kinetics
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Mice
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Microsomes / metabolism
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Models, Biological
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Molecular Chaperones / chemistry
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Molecular Chaperones / genetics
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Molecular Chaperones / metabolism*
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Molecular Sequence Data
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Mutagenesis, Site-Directed
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Neoplasm Proteins / chemistry*
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Neoplasm Proteins / genetics
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Neoplasm Proteins / metabolism*
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Peptides / metabolism
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Plasmids
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Protein Binding
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Recombinant Proteins / chemistry
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Recombinant Proteins / metabolism
Substances
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Carrier Proteins
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DnaJ protein, E coli
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Dnajc1 protein, mouse
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Endoplasmic Reticulum Chaperone BiP
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Escherichia coli Proteins
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HSP40 Heat-Shock Proteins
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HSP70 Heat-Shock Proteins
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Heat-Shock Proteins
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Hspa5 protein, mouse
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Molecular Chaperones
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Neoplasm Proteins
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Peptides
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Recombinant Proteins
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Adenosine Triphosphatases
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dnaK protein, E coli