Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Certain protein toxins, including cholera toxin, ricin, and Pseudomonas aeruginosa exotoxin A, are transported to the lumen of the endoplasmic reticulum where they retro-translocate across the endoplasmic reticulum membrane to enter the cytoplasm. The mechanism of retrotranslocation is poorly understood but may involve the endoplasmic reticulum-associated degradation pathway. The AAA ATPase p97 (also called valosin-containing protein) participates in the retro-translocation of cellular endoplasmic reticulum-associated degradation substrates and is therefore a candidate to participate in the retrotranslocation of protein toxins. To investigate whether p97 functions in toxin delivery to the cytoplasm, we measured the sensitivity to toxins of cells expressing either wild-type p97 or a dominant ATPase-defective p97 mutant under control of a tetracycline-inducible promoter. The rate at which cholera toxin and related toxins entered the cytoplasm was reduced in cells expressing the ATPase-defective p97, suggesting that the toxins might interact with p97. To detect interaction, the cholera toxin A chain was immunoprecipitated from cholera toxin-treated Vero cells, and co-immunoprecipitation of p97 was assessed by immunoblotting. The immunoprecipitates contained both cholera toxin A chain and p97, evidence that the two proteins are in a complex. Altogether, these results provide functional and structural evidence that p97 participates in the transport of cholera toxin to the cytoplasm.
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PMID:p97 Is in a complex with cholera toxin and influences the transport of cholera toxin and related toxins to the cytoplasm. 1569 47

Valosin-containing protein (VCP)/p97 is an AAA family ATPase that has been implicated in the removal of misfolded proteins from the endoplasmic reticulum and in membrane fusion. p97 forms a homohexamer whose protomers consist of an N-terminal (N) domain responsible for binding to effector proteins, followed by two AAA ATPase domains, D1 and D2. Small-angle X-ray scattering (SAXS) measurements of p97 in the presence of AMP-PNP (ATP state), ADP-AlF(x) (hydrolysis transition state), ADP, or no nucleotide reveal major changes in the positions of the N domains with respect to the hexameric ring during the ATP hydrolysis cycle. Nucleotide binding and hydrolysis experiments indicate that D2 inhibits nucleotide exchange by D1. The data suggest that the conversion of the chemical energy of ATP hydrolysis into mechanical work on substrates involves transmission of conformational changes generated by D2 through D1 to move N.
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PMID:Conformational changes of p97 during nucleotide hydrolysis determined by small-angle X-Ray scattering. 1569 59

The endoplasmic reticulum (ER) is the major intracellular membrane system. The ER is essential for protein and lipid biosynthesis, transport of proteins along the secretory pathway, and calcium storage. Here, we describe our investigations into the dynamics and regulation of the ER in the early Caenorhabditis elegans embryo. Using a GFP fusion to the ER-resident signal peptidase SP12, we observed the morphological transitions of the ER through fertilization and the early cell-cycles in living embryos. These transitions were tightly coordinated with the division cycle: upon onset of mitosis, the ER formed structured sheets that redispersed at the initiation of cleavage. Although microtubules were not required for the transition of the ER between these different states, the actin cytoskeleton facilitated the dispersal of the ER at the end of mitosis. The ER had an asymmetric distribution in the early embryo, which was dependent on the establishment of polarity by the PAR proteins. The small GTPase ARF-1 played an essential role in the ER dynamics, although this function appeared to be unrelated to the role of ARF-1 in vesicular traffic. In addition, the ER-resident heat shock protein BiP and a homologue of the AAA ATPase Cdc48/p97 were found to be crucial for the ER transitions. Both proteins have been implicated in homotypic ER membrane fusion. We provide evidence that homotypic membrane fusion is required to form the sheet structure in the early embryo.
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PMID:Involvement of the actin cytoskeleton and homotypic membrane fusion in ER dynamics in Caenorhabditis elegans. 1571 56

Misfolded or unassembled polypeptides in the endoplasmic reticulum (ER) are retro-translocated into the cytosol and degraded by the ubiquitin-proteasome system. We reported previously that the SCF(Fbs1,2) ubiquitin-ligase complexes that contribute to ubiquitination of glycoproteins are involved in the ER-associated degradation pathway. Here we investigated how the SCF(Fbs1,2) complexes interact with unfolded glycoproteins. The SCF(Fbs1) complex was associated with p97/VCP AAA ATPase and bound to integrin-beta1, one of the SCF(Fbs1) substrates, in the cytosol in a manner dependent on p97 ATPase activity. Both Fbs1 and Fbs2 proteins interacted with denatured glycoproteins, which were modified with not only high-mannose but also complex-type oligosaccharides, more efficiently than native proteins. Given that Fbs proteins interact with innermost chitobiose in N-glycans, we propose that Fbs proteins distinguish native from unfolded glycoproteins by sensing the exposed chitobiose structure.
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PMID:Glycoprotein-specific ubiquitin ligases recognize N-glycans in unfolded substrates. 1572 43

In mammalian cells, the Golgi apparatus and endoplasmic reticulum have typical structures during interphase: stacked cisternae located adjacent to the nucleus and a network of interconnected tubules throughout the cytoplasm, respectively. At mitosis their architectures disappear and are reassembled in daughter cells. p97, an AAA-ATPase, mediates membrane fusion and is required for reassembly of these organelles. In the p97-mediated membrane fusion, p47 was identified as an essential cofactor, through which p97 binds to a SNARE, syntaxin5. A second essential cofactor, VCIP135, was identified as a p97/p47/syntaxin5-interacting protein. Several lines of recent evidence suggest that ubiquitination may be implicated in the p97/p47 pathway; p47 binds to monoubiquitinated proteins and VCIP135 shows a deubiquitinating activity in vitro. For the cell-cycle regulation of the p97/p47 pathway, it has been reported that the localization and phosphorylation-dephosphorylation of p47 are crucial. In this review, we describe the components involved in the p97-mediated membrane fusion and discuss the regulation of the fusion pathway.
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PMID:p97/p47-Mediated biogenesis of Golgi and ER. 1574 24

The enzymatic A1 chain of cholera toxin retrotranslocates across the endoplasmic reticulum membrane into the cytosol, where it induces toxicity. Almost all other retrotranslocation substrates are modified by the attachment of polyubiquitin chains and moved into the cytosol by the ubiquitin-interacting p97 ATPase complex. The cholera toxin A1 chain, however, can induce toxicity in the absence of ubiquitination, and the motive force that drives retrotranslocation is not known. Here, we use adenovirus expressing dominant-negative mutants of p97 to test whether p97 is required for toxin action. We find that cholera toxin still functions with only a small decrease in potency in cells that cannot retrotranslocate other substrates at all. These results suggest that p97 does not provide the primary driving force for extracting the A1 chain from the endoplasmic reticulum, a finding that is consistent with a requirement for polyubiquitination in p97 function.
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PMID:Role of p97 AAA-ATPase in the retrotranslocation of the cholera toxin A1 chain, a non-ubiquitinated substrate. 1593 73

Inositol 1,4,5-trisphosphate (IP(3)) receptors form tetrameric, IP(3)-gated channels in endoplasmic reticulum membranes that govern the release of Ca(2+) from this organelle. In response to activation of certain G protein-coupled receptors that persistently elevate IP(3) concentration, IP(3) receptors are ubiquitinated and degraded by the ubiquitin-proteasome pathway. IP(3) receptor ubiquitination is mediated by the ubiquitin-conjugating enzyme, (mam)Ubc7, a component of the endoplasmic reticulum-associated degradation pathway. However, the mechanism by which ubiquitinated IP(3) receptors are transferred to the proteasome is not known. Here, we examine this process and show in several mammalian cell types that the ATPase p97 associates with IP(3) receptors in response to hormonal stimuli that induce IP(3) receptor ubiquitination. To examine the functional relevance of the p97 interaction with IP(3) receptors, we stably and specifically reduced p97 protein levels by 62 +/- 3% in Rat-1 fibroblasts using RNA interference. In these cells, endothelin-1-induced IP(3) receptor degradation was markedly retarded and the accumulation of ubiquitinated IP(3) receptors was markedly enhanced. These effects were reversed by expression of exogenous p97. In addition, Ufd1 and Npl4, which complex with p97, also associated with IP(3) receptors upon hormonal stimulation. We conclude that the p97-Ufd1-Npl4 complex couples ubiquitinated IP(3) receptors to proteasomal degradation and, thus, plays a key role in IP(3) receptor processing. These data also establish that the p97-Ufd1-Npl4 complex mediates endoplasmic reticulum-associated degradation in mammalian cells.
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PMID:Involvement of the p97-Ufd1-Npl4 complex in the regulated endoplasmic reticulum-associated degradation of inositol 1,4,5-trisphosphate receptors. 1610 11

Endoplasmic reticulum (ER)-associated protein degradation (ERAD) is a quality control system that removes misfolded proteins from the ER. ERAD substrates are channelled from the ER via a proteinacious pore to the cytosolic ubiquitin-proteasome system - a process involving dedicated ubiquitin ligases and the chaperone-like AAA ATPase Cdc48 (also known as p97). How the activities of these proteins are coupled remains unclear. Here we show that the UBX domain protein Ubx2 is an integral ER membrane protein that recruits Cdc48 to the ER. Moreover, Ubx2 mediates binding of Cdc48 to the ubiquitin ligases Hrd1 and Doa10, and to ERAD substrates. In addition, Ubx2 and Cdc48 interact with Der1 and Dfm1, yeast homologues of the putative dislocation pore protein Derlin-1 (refs 11-13). Lack of Ubx2 causes defects in ERAD that are exacerbated under stress conditions. These findings are consistent with a model in which Ubx2 coordinates the assembly of a highly efficient ERAD machinery at the ER membrane.
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PMID:Membrane-bound Ubx2 recruits Cdc48 to ubiquitin ligases and their substrates to ensure efficient ER-associated protein degradation. 1617 52

Endoplasmic reticulum (ER)-associated protein degradation requires the dislocation of selected substrates from the ER to the cytosol for proteolysis via the ubiquitin-proteasome system. The AAA ATPase Cdc48 (known as p97 or VCP in mammals) has a crucial, but poorly understood role in this transport step. Here, we show that Ubx2 (Sel1) mediates interaction of the Cdc48 complex with the ER membrane-bound ubiquitin ligases Hrd1 (Der3) and Doa10. The membrane protein Ubx2 contains a UBX domain that interacts with Cdc48 and an additional UBA domain. Absence of Ubx2 abrogates breakdown of ER proteins but also that of a cytosolic protein, which is ubiquitinated by Doa10. Intriguingly, our results suggest that recruitment of Cdc48 by Ubx2 is essential for turnover of both ER and non-ER substrates, whereas the UBA domain of Ubx2 is specifically required for ER proteins only. Thus, a complex comprising the AAA ATPase, a ubiquitin ligase and the recruitment factor Ubx2 has a central role in ER-associated proteolysis.
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PMID:Ubx2 links the Cdc48 complex to ER-associated protein degradation. 1617 53

Polypeptides that fail to pass quality control in the endoplasmic reticulum (ER) are dislocated from the ER membrane to the cytosol where they are degraded by the proteasome. Derlin-1, a member of a family of proteins that bears homology to yeast Der1p, was identified as a factor that is required for the human cytomegalovirus US11-mediated dislocation of class I MHC heavy chains from the ER membrane to the cytosol. Derlin-1 acts in concert with the AAA ATPase p97 to remove dislocation substrate proteins from the ER membrane, but it is unknown whether other factors aid Derlin-1 in its function. Mammalian genomes encode two additional, related proteins (Derlin-2 and Derlin-3). The similarity of the mammalian Derlin-2 and Derlin-3 proteins to yeast Der1p suggested that these as-yet-uncharacterized Derlins also may play a role in ER protein degradation. We demonstrate here that Derlin-2 is an ER-resident protein that, similar to Derlin-1, participates in the degradation of proteins from the ER. Furthermore, we show that Derlin-2 forms a robust multiprotein complex with the p97 AAA ATPase as well as the mammalian orthologs of the yeast Hrd1p/Hrd3p ubiquitin-ligase complex. The data presented here define a set of interactions between proteins involved in dislocation of misfolded polypeptides from the ER.
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PMID:Multiprotein complexes that link dislocation, ubiquitination, and extraction of misfolded proteins from the endoplasmic reticulum membrane. 1618 9


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