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Query: UNIPROT:P11021 (BiP)
 2,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A complex array of chaperones and enzymes reside in the endoplasmic reticulum (ER) to assist the folding and assembly of and the disulfide bond formation in nascent secretory proteins. Here we characterize a novel human putative ER co-chaperone (ERdj5) containing domains resembling DnaJ, protein-disulfide isomerase, and thioredoxin domains. Homologs of ERdj5 have been found in Caenorhabditis elegans and Mus musculus. In vitro experiments demonstrated that ERdj5 interacts via its DnaJ domain with BiP in an ATP-dependent manner. ERdj5 is a ubiquitous protein localized in the ER and is particularly abundant in secretory cells. Its transcription is induced during ER stress, suggesting potential roles for ERdj5 in protein folding and translocation across the ER membrane.
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PMID:ERdj5, an endoplasmic reticulum (ER)-resident protein containing DnaJ and thioredoxin domains, is expressed in secretory cells or following ER stress. 1241 43

Several endoplasmic reticulum (ER)-resident luminal proteins have a characteristic ER retrieval signal, KDEL, or its variants at their C terminus. Our previous work searching EST databases for proteins containing the C-terminal KDEL motif predicted some novel murine proteins, one of which designated JPDI (J-domain-containing protein disulfide isomerase-like protein) is characterized in this study. The primary structure of JPDI is unique, because in addition to a J-domain motif adjacent to the N-terminal translocation signal sequence, four thioredoxin-like motifs were found in a single polypeptide. As examined by Northern blotting, the expression of JPDI was essentially ubiquitous in tissues and almost independent of ER stress. A computational prediction that JPDI is an ER-resident luminal protein was experimentally supported by immunofluorescent staining of epitope-tagged JPDI-expressing cells together with glycosylation and protease protection studies of this protein. JPDI probably acts as a DnaJ-like partner of BiP, because a recombinant protein carrying the J-domain of JPDI associated with BiP in an ATP-dependent manner and enhanced its ATPase activity. We speculate that for the folding of some proteins in the ER, chaperoning by BiP and formation of proper disulfide bonds may synchronously occur in a JPDI-dependent manner.
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PMID:JPDI, a novel endoplasmic reticulum-resident protein containing both a BiP-interacting J-domain and thioredoxin-like motifs. 1244 77

In this study, we demonstrate that the folding and assembly of IgG in transgenic tobacco plants is orchestrated by BiP (binding protein), an endoplasmic reticulum resident chaperone. Expression of BiP and calreticulin was examined in transgenic tobacco plants that express immunoglobulin chains, either singly or in combination to form IgG antibody. BiP mRNA expression was lowest in wild-type nontransformed plants and those that expressed immunoglobulin light chain alone. Higher mRNA levels were detected in plants expressing fully assembled immunoglobulin (light and heavy chains), and the most abundant levels of RNA transcript were found in those plants that expressed immunoglobulin heavy chain alone. Estimation of total BiP demonstrated a similar pattern, with the highest levels detected in plants expressing immunoglobulin heavy chain alone. Immunoprecipitation studies demonstrated that BiP was associated with immunoglobulin chains extracted from protoplast lysates, but not from secreted fluids. Again, most BiP was coprecipitated from plants expressing heavy chain only and those that produced full length IgG. The binding of BiP to Ig heavy chains was ATP-sensitive. Co-expression of heavy and light chain resulted in IgG assembly and displacement of BiP from the heavy chain as the amount of light chain increased. Although calreticulin mRNA and total protein levels varied in a similar manner to those of BiP in the transgenic plants, there was no evidence for association between calreticulin and Ig chains, by coimmunoprecipitation. The results indicate that BiP, but not calreticulin, takes part in immunoglobulin folding and assembly in transgenic plants.
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PMID:ER-resident chaperone interactions with recombinant antibodies in transgenic plants. 1247

BiP, the Hsp70 homologue of the endoplasmic reticulum, interacts with its non-native substrate proteins in an ATP-dependent manner. This interaction is coupled to the ATPase cycle of the chaperone. Binding of short, synthetic peptides stimulate the ATPase activity of BiP. In previous work, we showed that a stably unfolded antibody domain forms a binary complex with BiP. In this study we made use of this complex to analyse the effect of substrate proteins on the ATPase cycle of BiP. Kinetic constants of the partial reactions of the ATPase cycle were determined without substrate, in the presence of a short binding peptide and in the presence of the antibody domain. We show that, in contrast to smaller peptides, the non-native protein domain decelerates the rate limiting hydrolysis step of the ATPase cycle.
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PMID:Modulation of the ATPase cycle of BiP by peptides and proteins. 1281 8

Aggregation occurs through hydrophobic interactions when a polypeptide chain refolds in non-native states or when genetic variants of biologically active proteins assume inappropriate conformations, as observed in the case of dysfunctional serpins. Here, using the molecular chaperone BiP from bovine liver microsomes, we characterized the hydrophobic nature of the peptide segment which is considered to be a site required for aggregation among a non-inhibitory serpin ovalbumin in a heat-denatured state. Screening of the peptide scan for binding of BiP showed that BiP-binding sites are mostly buried in the folded ovalbumin. When ovalbumin was heat-denatured, the denatured protein was recognized by the antibody that reacts with the hydrophobic surface of the amino-terminal segment of ovalbumin. This antibody significantly suppressed the binding of BiP to denatured ovalbumin. BiP also bound the immobilized peptide in an ATP-dependent manner and the peptide stimulated the ATPase activity of BiP with a Km of 165 microM and a Vmax of 0.4 nmol/min per milligram. Measurement of surface plasmon resonance showed that the peptide had a Kd of 0.52 microM by BiP, lower than that for RCMLA (Kd = 1.1 microM) and even lower than that of the peptide P10K, PLSRTLSVAAKK, (Kd = 21 microM). These results demonstrate that the aggregation-prone site on heat-denatured ovalbumin has almost the same hydrophobic nature of interacting with the molecular chaperone BiP as the conventionally known peptides that bind to the Escherichia coli chaperone DnaK.
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PMID:Analysis of molecular interactions in heat-induced aggregation of a non-inhibitory serpin ovalbumin using a molecular chaperone. 1283 80

The endoplasmic reticulum (ER) possesses the structural and functional features expected of an organelle that supports the integration and coordination of major cellular processes. Ca(2+) sequestered within the ER sustains lumenal protein processing while providing a reservoir of the cation to support stimulus-response coupling in the cytosol. Release of ER Ca(2+) sufficient to impair protein processing promotes ER stress and signals the "unfolded protein response" (UPR). The association of the UPR with an acute suppression of mRNA translational initiation and a longer term up-regulation of ER chaperones and partial translational recovery is discussed. Regulatory sites in mRNA translation and the mechanisms responsible for the early and later phases of the UPR are reviewed. The regulatory significance of GRP78/BiP, a multifunctional, broad-specificity ER chaperone, in the coordination of ER protein processing with mRNA translation during acute and chronic ER stress is addressed. The relationship of ER stress to protein misfolding in the cytoplasm is examined. Translational alterations in embryonic cardiomyocytes during treatments with various Ca(2+)-mobilizing, growth-promoting stimuli are described. The importance of ER Ca(2+) stores, ER chaperones, and cytosolic-free Ca(2+) in translational control and growth promotion by these stimuli is assessed. Some perspectives are provided regarding Ca(2+) as an integrating factor in the generation or diversion of metabolic energy. Circumstances impacting upon cellular adaptability during exposure to growth stimuli or during stressful conditions that require rapid adjustments in ATP for continued viability are considered.
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PMID:Calcium dynamics and endoplasmic reticular function in the regulation of protein synthesis: implications for cell growth and adaptability. 1290 81

Dislocation of endoplasmic reticulum-associated degradation (ERAD) substrates from the endoplasmic reticulum (ER) lumen to cytosol is considered to occur in a single step that is tightly coupled to proteasomal degradation. Here we show that dislocation of luminal ERAD substrates occurs in two distinct consecutive steps. The first is passage across ER membrane to the ER cytosolic face, where substrates can accumulate as ubiquitin conjugates. In vivo, this step occurs despite proteasome inhibition but requires p97/Cdc48p because substrates remain entrapped in ER lumen and are prevented from ubiquitination in cdc48 yeast strain. The second dislocation step is the release of accumulated substrates to the cytosol. In vitro, this release requires active proteasome, consumes ATP, and relies on salt-removable ER-bound components, among them the ER-bound p97 and ER-bound proteasome, which specifically interact with the cytosol-facing substrates. An additional role for Cdc48p subsequent to ubiquitination is revealed in the cdc48 strain at permissive temperature, consistent with our finding that p97 recognizes luminal ERAD substrates through multiubiquitin. BiP interacts exclusively with ERAD substrates, suggesting a role for this chaperone in ERAD. We propose a model that assigns the cytosolic face of the ER as a midpoint to which luminal ERAD substrates emerge and p97/Cdc48p and the proteasome are recruited. Although p97/Cdc48p plays a dual role in dislocation and is involved both in passage of the substrate across ER membrane and subsequent to its ubiquitination, the proteasome takes part in the release of the substrate from the ER face to the cytosol en route to degradation.
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PMID:Distinct steps in dislocation of luminal endoplasmic reticulum-associated degradation substrates: roles of endoplamic reticulum-bound p97/Cdc48p and proteasome. 1460 30

Cholera toxin (CT) is transported from the cell surface to the endoplasmic reticulum (ER) from where it is translocated to the cytosol in a process depending on ATP and luminal ER proteins. To test whether the molecular chaperone BiP (heavy chain binding protein), which is an ER-luminal ATPase, was one of the required proteins the export of CT was analyzed using ER-derived CT-loaded microsomes. The resubstitution of extracted export-incompetent microsomes with purified BiP was sufficient to restore the export of CT. As BiP protected CT from aggregation it is proposed that BiP maintains CT in a soluble, export-competent state.
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PMID:BiP-dependent export of cholera toxin from endoplasmic reticulum-derived microsomes. 1462 8

We present a model of a generalizable but minimalistic network based on the properties of interactions between proteins, molecular chaperones (e.g., Hsp70, BiP) and ATP inside cells and subcellular components such as endoplasmic reticulum (ER). The dynamics of chaperone-dependent protein folding and misfolding in the cell can be modeled mathematically as a "predator-prey" problem, which can then be used to analyze the behavior of the system under conditions simulating stress (e.g., cardiac ischemia). We have tested this model under normal physiological and diseased conditions (e.g., ischemia as simulated by ATP depletion) and analyzed the effects of induction of chaperones (e.g., heat shock, tunicamycin) and inhibition of the degradative pathway (e.g., proteasome inhibition) on this model. Simulation gave the following results: (1) Under normal physiological conditions, as expected, the model predicts the stable production of correctly folded proteins. (2) A threshold of ATP levels exists below which the system tends toward increasing degrees of complex behavior. When ATP levels are just above this threshold, the system is highly vulnerable to sudden, brief drops in ATP levels such as may occur in the setting of acute ischemia: bursts of oscillations continue even when ATP levels revert to the threshold. However, if ATP levels are rapidly increased to levels considerably above the threshold, the system becomes stable again. (3) Up to 10-fold increases in chaperone levels, such as those that occur under conditions of prior heat shock or tunicamycin treatment, did not affect the behavior of the system under basal conditions, nor did it affect the tendency to complex behavior in the setting of ATP depletion. It did, however, shorten the recovery period of the system after chaotic-type oscillations were induced by acute ATP depletion. (4) Blocking the degradative pathway for misfolded proteins (e.g., proteasome inhibition) predisposes the system toward instability in the setting of ATP depletion by changing the ATP threshold at which bursts of oscillations occur. These results support the hypothesis that there are distinct thresholds for ATP, chaperones, and degradative activity, outside which cellular protein folding dynamics become unstable. They also suggest that an important mechanism by which chaperone induction protects cells from subsequent stress is by limiting the tendency to instability after an insult (e.g., acute myocardial ischemia or acute tubular injury to the kidney).
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PMID:Complex dynamics of chaperone-protein interactions under cellular stress. 1521 Oct 27

In mammalian cells, factor VIII (FVIII) secretion depends upon its interaction with chaperones of the endoplasmic reticulum (ER) and requires a unique ATP-dependent step to dissociate aggregates formed within the ER. To further elucidate mechanisms which might account for the inefficient secretion of recombinant FVIII (rFVIII), we have analyzed the pathways of recombinant full length (rFVIII-FL) and B-domain deleted (rFVIII Delta B) FVIII and compared these to the secretion route of native FVIII in primary hepatocytes. Using confocal laser scanning microscopy in combination with a pulse chase of a known secretion marker, we describe the trafficking route of FVIII, which upon release from the ER--where it colocalizes with calnexin--is transported to the Golgi complex in vesicular-tubular transport complexes (VTCs) which could be further identified as being COP I coated. However, a large portion of rFVIII is retained in the ER and additionally in structures which could not be assigned to the ER, Golgi complex or intermediate compartment. Moderate BiP transcription levels indicate that this observed retention of FVIII does not reflect cellular stress due to an overexpression of FVIII-protein in transduced cells. Moreover, a pulse of newly synthesized rFVIII protein is released within 4 hrs, indicating that once rFVIII is released from the ER there is no further limitation to its secretion. Our data provide new details about the secretory route of FVIII, which may ultimately help to identify factors currently limiting the efficient and physiological expression of FVIII in gene therapy and manufacture.
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PMID:Confocal microscopy analysis of native, full length and B-domain deleted coagulation factor VIII trafficking in mammalian cells. 1521 41


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