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Query: UNIPROT:P50502 (Hip)
 7,003 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Heat shock protein 90 (Hsp90) is a molecular chaperone involved in the folding and assembly of a limited set of "client" proteins, many of which are involved in signal transduction pathways. In vivo, it is found in complex with additional proteins, including the chaperones Hsp70, Hsp40, Hip and Hop (Hsp-interacting and Hsp-organising proteins, respectively), as well as high molecular mass immunophilins, such as FKBP59, and the small acidic protein p23. The role of these proteins in Hsp90-mediated assembly processes is poorly understood. It is known that ATP binding and hydrolysis are essential for Hsp90 function in vivo and in vitro. Here we show, for the first time, that human Hsp90 has ATPase activity in vitro. The ATPase activity is characterised using a sensitive assay based on a chemically modified form of the phosphate-binding protein from Escherichia coli. Human Hsp90 is a very weak ATPase, its activity is significantly lower than that of the yeast homologue, and it has a half-life of ATP hydrolysis of eight minutes at 37 degrees C. Using a physiological substrate of Hsp90, the ligand-binding domain of the glucocorticoid receptor, we show that this "client" protein can stimulate the ATPase activity up to 200-fold. This effect is highly specific and unfolded or partially folded proteins, which are known to bind to Hsp90, do not affect the ATPase activity. In addition, the peroxisome proliferator-activated receptor, which is related in both sequence and structure to the glucocorticoid receptor but which does not bind Hsp90, has no observable effect on the ATPase activity. We establish the effect of the co-chaperones Hop, FKBP59 and p23 on the basal ATPase activity as well as the client protein-stimulated ATPase activity of human Hsp90. In contrast with the yeast system, human Hop has little effect on the basal rate of ATP hydrolysis but significantly inhibits the client-protein stimulated rate. Similarly, FKBP59 has little effect on the basal rate but stimulates the client-protein stimulated rate further. In contrast, p23 inhibits both the basal and stimulated rates of ATP hydrolysis. Our results show that the ATPase activity of human Hsp90 is highly regulated by both client protein and co-chaperone binding. We suggest that the rate of ATP hydrolysis is critical to the mode of action of Hsp90, consistent with results that have shown that both over and under-active ATPase mutants of yeast Hsp90 have impaired function in vivo. We suggest that the tight regulation of the ATPase activity of Hsp90 is important and allows the client protein to remain bound to Hsp90 for sufficient time for activation to occur.
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PMID:Stimulation of the weak ATPase activity of human hsp90 by a client protein. 1181 47

We reported previously that the human RNF2 (RING finger protein 2) protein is an E3 ubiquitin ligase that interacts with the human ubiquitin-conjugating enzyme Hip-2/hE2-25K. In the present study, we show that RNF2 interacts with S6' ATPase, a subunit of the proteasomal 19 S regulatory complex. S6' interacts with RNF2 through its N-terminal RING domain, and RNF2 interacts with S6' through its C-terminal region. Interestingly, the RNF2-S6' interaction increases the ATP hydrolysis activity of the S6' protein. Moreover, S6' ATPase activity is highly increased in the presence of ubiquitinated proteins. The present study suggests that the E3 ubiquitin ligase RNF2 might have a dual function: facilitating the ubiquitination of its target substrates and recruiting the substrates to the proteasome. Furthermore, ATP hydrolysis in the E3/proteasome complex might act as an important signal for the protein degradation pathway.
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PMID:E3 ubiquitin ligase RNF2 interacts with the S6' proteasomal ATPase subunit and increases the ATP hydrolysis activity of S6'. 1577 19

Her-2/neu (ErbB2) is a transmembrane tyrosine kinase and acts as a co-receptor for the other EGFR family members. It is well known that high expression of Her-2/neu is associated with a poor prognosis in breast cancer. Quercetin, a flavonoid present in many vegetables and fruits, has been studied extensively as a chemoprevention agent in several cancer models. In this study, we observed that quercetin decreased the level of Her-2/neu protein in time- and dose-dependent manners and also inhibited the downstream survival PI3K-Akt signaling pathway in Her-2/neu-overexpressing breast cancer SK-Br3 cells. We also observed that quercetin induced polyubiquitination of Her-2/neu. When the proteasome pathway was blocked by MG-132 during quercetin treatment, accumulation of the NP-40 insoluble form of Her-2/neu occurred. Interestingly, data from immunocomplex studies revealed that quercetin promoted interaction between Her-2/neu and Hsp90 which is a molecular chaperone involved in stabilization of Her-2/neu. In this condition, inhibition of Hsp90 activity by a specific inhibitor, geldanamycin (GA), or intracellular ATP depletion caused dissociation of Hsp90 from Her-2/neu and promoted ubiquitination and down-regulation of Her-2/neu protein. In addition, the carboxyl terminus of Hsc70-interacting protein (CHIP), a chaperone-dependent E3 ubiquitin ligase, played a crucial role in the quercetin-induced ubiquitination of Her-2/neu. Inhibition of tyrosine kinase activity of Her-2/neu by quercetin could indicate an lateration in the Her-2/neu structure which promotes CHIP recruitments and down-regulation of Her-2/neu. We believe that by using quercetin, new therapeutic strategies can be developed to treat Her-2/neu overexpressing cancers.
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PMID:Quercetin-induced ubiquitination and down-regulation of Her-2/neu. 1865 87

The ATP-dependent protein chaperone heat-shock protein 70 (Hsp70) displays broad anti-aggregation functions and has a critical function in preventing protein misfolding pathologies. According to in vitro and in vivo models of Parkinson's disease (PD), loss of Hsp70 activity is associated with neurodegeneration and the formation of amyloid deposits of alpha-synuclein (alphaSyn), which constitute the intraneuronal inclusions in PD patients known as Lewy bodies. Here, we show that Hsp70 depletion can be a direct result of the presence of aggregation-prone polypeptides. We show a nucleotide-dependent interaction between Hsp70 and alphaSyn, which leads to the aggregation of Hsp70, in the presence of ADP along with alphaSyn. Such a co-aggregation phenomenon can be prevented in vitro by the co-chaperone Hip (ST13), and the hypothesis that it might do so also in vivo is supported by studies of a Caenorhabditis elegans model of alphaSyn aggregation. Our findings indicate that a decreased expression of Hip could facilitate depletion of Hsp70 by amyloidogenic polypeptides, impairing chaperone proteostasis and stimulating neurodegeneration.
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PMID:Chaperone proteostasis in Parkinson's disease: stabilization of the Hsp70/alpha-synuclein complex by Hip. 1987 82

The E3 ubiquitin ligase CHIP (C-terminus of Hsc70-interacting protein) is believed to be a central player in the cellular triage decision, as it links the molecular chaperones Hsp70/Hsc70 and Hsp90 to the ubiquitin proteasomal degradation pathway. To better understand the decision process, we determined the affinity of CHIP for Hsp70 and Hsp90 using isothermal titration calorimetry. We analyzed the influence of CHIP on the ATPase cycles of both chaperones in the presence of co-chaperones and a substrate, and determined the ubiquitination efficacy of CHIP in the presence of the chaperones. We found that CHIP has a sixfold higher affinity for Hsp90 compared with Hsc70. CHIP had no influence on ADP dissociation or ATP association, but reduced the Hsp70 cochaperone Hdj1-stimulated single-turnover ATPase rates of Hsc70 and Hsp70. CHIP did not influence the ATPase cycle of Hsp90 in the absence of co-chaperones or in the presence of the Hsp90 cochaperones Aha1 or p23. Polyubiquitination of heat-denatured luciferase and the native substrate p53 was much more efficient in the presence of Hsc70 and Hdj1 than in the presence of Hsp90, indicating that CHIP preferentially ubiquitinates Hsp70-bound substrates.
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PMID:CHIP participates in protein triage decisions by preferentially ubiquitinating Hsp70-bound substrates. 2061 41

The Hsp70-interacting protein, Hip, cooperates with the chaperone Hsp70 in protein folding and prevention of aggregation. Hsp70 interacts with non-native protein substrates in an ATP-dependent reaction cycle regulated by J-domain proteins and nucleotide exchange factors (NEFs). Hip is thought to delay substrate release by slowing ADP dissociation from Hsp70. Here we present crystal structures of the dimerization domain and the tetratricopeptide repeat (TPR) domain of rat Hip. As shown in a cocrystal structure, the TPR core of Hip interacts with the Hsp70 ATPase domain through an extensive interface, to form a bracket that locks ADP in the binding cleft. Hip and NEF binding to Hsp70 are mutually exclusive, and thus Hip attenuates active cycling of Hsp70-substrate complexes. This mechanism explains how Hip enhances aggregation prevention by Hsp70 and facilitates transfer of specific proteins to downstream chaperones or the proteasome.
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PMID:Structure and function of Hip, an attenuator of the Hsp70 chaperone cycle. 2381 73

Mitochondrial kinase PTEN-induced putative kinase 1 (PINK1) and E3 ubiquitin ligase Parkin function in a common pathway to regulate mitochondrial homeostasis contributing to the pathogenesis of Parkinson disease. The carboxyl terminus of Hsc70-interacting protein (CHIP) acts as a heat shock protein 70/heat shock protein 90 cochaperone to mediate protein folding or as an E3 ubiquitin ligase to target proteins for degradation. In this study, overexpression of Drosophila CHIP suppressed a range of Pink1 mutant phenotypes in flies, including abnormal wing posture, thoracic indentation, locomotion defects, muscle degeneration, and loss of dopaminergic neurons. Mitochondrial defects of Pink1 mutant, such as excessive fusion, reduced ATP content, and crista disorganization, were rescued by CHIP but not its ligase-dead mutants. Similar phenotypes and mitochondrial impairment were ameliorated in Parkin mutant flies by wild-type CHIP. Inactivation of CHIP with null fly mutants resulted in mitochondrial defects, such as reduced thoracic ATP content at 3 d old, decreased thoracic mitochondrial DNA content, and defective mitochondrial morphology at 60 d old. CHIP mutants did not exacerbate the phenotypes of Pink1 mutant flies but markedly shortened the life span of Parkin mutant flies. These results indicate that CHIP is involved in mitochondrial integrity and may act downstream of Pink1 in parallel with Parkin.-Chen, J., Xue, J., Ruan, J., Zhao, J., Tang, B., Duan, R. Drosophila CHIP protects against mitochondrial dysfunction by acting downstream of Pink1 in parallel with Parkin.
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PMID:Drosophila CHIP protects against mitochondrial dysfunction by acting downstream of Pink1 in parallel with Parkin. 2877 78

One of the major mechanisms followed by the therapeutic agents to target the causative organism of TB, mycobacterium tuberculosis (Mtb), involves disruption of the replication cycle of the pathogen DNA. The process involves two steps that occur simultaneously, ie, breakage and reunion of DNA at gyrase A (GyrA) domain and ATP hydrolysis at gyrase B (GyrB) domain. Current therapy for multi-drug resistant TB involves FDA approved, Fluoroquinolone-based antibiotics, which act by targeting the replication process at GyrA domain. However, resistance against fluoroquinolones due to mutations in the GyrA domain has limited the use of this therapy and shifted the focus of the research community on the GyrB domain. Thus, this study involves in silico designing of chemotherapeutic agents for resistant TB by targeting GyrB domain. In the current study, a pharmacophore model for GyrB domain was generated using reported inhibitors. It was utilized as a query search against three commercial databases to identify GyrB domain inhibitors. Additionally, a qualitative Hip-Hop pharmacophore model for GyrA was also developed on the basis of some marketed fluoroquinolone-based GyrA inhibitors, to remove non-selective gyrase inhibitors obtained in virtual screening. Further, molecular dynamic simulations were carried out to determine the stability of the obtained molecules in complex with both the domains. Finally, Molecular mechanics with generalized Born and surface area solvation score was calculated to determine the binding affinity of obtained molecule with both domains to determine the selectivity of the obtained molecules that resulted in seven putative specific inhibitors of GyrB domain.
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PMID:Pharmacophore modeling and molecular dynamics approach to identify putative DNA Gyrase B inhibitors for resistant tuberculosis. 3019 89

One of the major mechanisms followed by the therapeutic agents to target the causative organism of TB, Mycobacterium tuberculosis, involves disruption of its DNA replication cycle. The process of replication involves two steps, i.e., breakage and reunion of DNA at gyrase A (GyrA) domain and ATP hydrolysis at gyrase B (GyrB) domain, both occur simultaneously. Current therapy for multi-drug resistant TB (MDR-TB) involves FDA approved, fluoroquinolone-based antibiotics, which act by targeting replication process at GyrA domain. However, resistance against fluoroquinolones due to mutations in the GyrA domain has limited the use of this therapy and shifted the focus of research community on GyrB domain. Thus, in the present study novel chemotherapeutic agents for resistant TB were designed by exploring GyrB domain using in silico techniques. Pharmacophore model of GyrB domain was employed for screening an In-house database. Followed by cross-screening via a qualitative Hip-Hop pharmacophore model for GyrA to remove non-selective gyrase B inhibitors. Further molecular dynamics simulations and MM-GBSA calculations were performed to determine stability and binding affinity of the screened molecules. These analyses resulted in five putative oxindole based selective GyrB domain inhibitors, which were synthesized and evaluated for anti-tubercular activity against M. tuberculosis H37Rv strain. Two compounds exhibited significant anti-TB activity, whereas other three compounds were found to be outliers of the in silico study.
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PMID:In silico designing of domain B selective gyrase inhibitors for effective treatment of resistant tuberculosis. 3020 73


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