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)

The Saccharomyces cerevisiae [PSI(+)] prion is believed to be a self-propagating cytoplasmic amyloid. Earlier characterization of HSP70 (SSA1) mutations suggested that [PSI(+)] propagation is impaired by alterations that enhance Ssa1p's substrate binding. This impairment is overcome by second-site mutations in Ssa1p's conserved C-terminal motif (GPTVEEVD), which mediates interactions with tetratricopeptide repeat (TPR) cochaperones. Sti1p, a TPR cochaperone homolog of mammalian Hop1 (Hsp70/90 organizing protein), activates Ssa1p ATPase, which promotes substrate binding by Ssa1p. Here we find that in SSA1-21 cells depletion of Sti1p improved [PSI(+)] propagation, while excess Sti1p weakened it. In contrast, depletion of Fes1p, a nucleotide exchange factor for Ssa1p that facilitates substrate release, weakened [PSI(+)] propagation, while overproducing Fes1p improved it. Therefore, alterations of Hsp70 cochaperones that promote or prolong Hsp70 substrate binding impair [PSI(+)] propagation. We also find that the GPTVEEVD motif is important for physical interaction with Hsp40 (Ydj1p), another Hsp70 cochaperone that promotes substrate binding but is dispensable for viability. We further find that depleting Cpr7p, an Hsp90 TPR cochaperone and CyP-40 cyclophilin homolog, improved [PSI(+)] propagation in SSA1 mutants. Although Cpr7p and Sti1p are Hsp90 cochaperones, we provide evidence that Hsp90 is not involved in [PSI(+)] propagation, suggesting that Sti1p and Cpr7p functionally interact with Hsp70 independently of Hsp90.
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PMID:Propagation of Saccharomyces cerevisiae [PSI+] prion is impaired by factors that regulate Hsp70 substrate binding. 1508 86

The heat shock protein Hsp90 plays a key, but poorly understood role in the folding, assembly and activation of a large number of signal transduction molecules, in particular kinases and steroid hormone receptors. In carrying out these functions Hsp90 hydrolyses ATP as it cycles between ADP- and ATP-bound forms, and this ATPase activity is regulated by the transient association with a variety of co-chaperones. Cdc37 is one such co-chaperone protein that also has a role in client protein recognition, in that it is required for Hsp90-dependent folding and activation of a particular group of protein kinases. These include the cyclin-dependent kinases (Cdk) 4/6 and Cdk9, Raf-1, Akt and many others. Here, the biochemical details of the interaction of human Hsp90 beta and Cdc37 have been characterised. Small angle X-ray scattering (SAXS) was then used to study the solution structure of Hsp90 and its complexes with Cdc37. The results suggest a model for the interaction of Cdc37 with Hsp90, whereby a Cdc37 dimer binds the two N-terminal domain/linker regions in an Hsp90 dimer, fixing them in a single conformation that is presumably suitable for client protein recognition.
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PMID:Biochemical and structural studies of the interaction of Cdc37 with Hsp90. 1522 29

The heat shock protein Hsp90 has increasingly become an important therapeutic target especially for treatment of cancers. Inhibition of the ATPase activity of Hsp90 by natural products (e.g., 17-allylaminogeldanamycin or radicicol) leads to the ubiquitination of oncogenic client proteins such as Her-2, Raf-1, and p-Akt followed by their proteasomal degradation. Hsp90 inhibitors simultaneously target multiple oncogenic proteins and provide an advantage for cancer therapy due to the potential for increased efficacy and overcoming drug resistance. In an effort to convert geldanamycin into a druglike compound with better pharmacokinetic properties and efficacy in human tumor xenograft models, geldanamycin was derivatized on the 17-position to prepare new analogues such as 17-geldanamycin amides, carbamates, and ureas and 17-arylgeldanamycins. All the compounds were first evaluated ex vivo using a cell-based Her-2 degradation assay and in vitro using biochemical assays that measure recombinant Hsp90 (rHsp90) competitive binding and changes in rHsp90 conformation. In addition, we confirmed the selectivity of geldanamycin analogues for Hsp90 derived from tumor cells using a novel cell lysate binding assay.
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PMID:Synthesis and biological evaluation of a new class of geldanamycin derivatives as potent inhibitors of Hsp90. 1523 64

Aryl hydrocarbon receptor (AhR) is a transcription factor that is activated by the binding of xenobiotic and endogenous ligands. AhR interacts with heat shock protein (Hsp) 90 complexes and can be used as a functional substrate to detect chaperone-dependent processes. Yeast Hsp90 (hsp82) mutants that variably affected AhR signaling were identified using reporter gene assays. Some mutated alleles resided in the p23/adenosine triphosphate (ATP)-binding pocket of Hsp90, so the relationship between the cochaperone Sba1 (yeast p23) and adenosine triphosphatase (ATPase) activity was investigated. Deletion of the p23 gene in the hsp82G170D mutant background had a greater effect on AhR signaling than the individual mutations, suggesting that these 2 mutations have separate actions on AhR signaling. In contrast, p23 overexpression suppressed temperature sensitivity and AhR signaling defects in the hsp82G170D mutant strain, suggesting that there is a relationship between these 2 proteins. The mutated hsp82G170D protein lacked detectable ATPase activity and p23 binding in vitro, which may relate to the weakened AhR signaling observed in mutant cells. Sba1 (p23) suppressed Hsp82 ATPase activity in vitro. These studies implicate the p23 protein and the G170 region of Hsp90 as being important, but not essential, for AhR signaling. Our results are consistent with a model in which p23 inhibits Hsp90 ATPase activity, thereby stabilizing ATP-Hsp90-client protein complexes.
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PMID:Cooperation of heat shock protein 90 and p23 in aryl hydrocarbon receptor signaling. 1527 73

Immortalized human fibroblasts were used to investigate the putative interactions of the Hsp90 molecular chaperone with the wild-type p53 tumor suppressor protein. We show that geldanamycin or radicicol, specific inhibitors of Hsp90, diminish specific wild-type p53 binding to the p21 promoter sequence. Consequently, these inhibitors decrease p21 mRNA levels, which lead to a reduction in cellular p21/Waf1 protein, known to induce cell cycle arrest. In control experiments, we show that neither geldanamycin nor radicicol affect p53 mRNA levels. A minor decrease in p53 protein level following the treatment of human fibroblasts with the inhibitors suggests the potential involvement of Hsp90 in the stabilization of wild-type p53. To support our in vivo findings, we used a reconstituted system with highly purified recombinant proteins to examine the effects of Hsp90 on wild-type p53 binding to the p21 promoter sequence. The human recombinant Hsp90 alpha-isoform as well as bovine brain Hsp90 were purified to homogeneity. Both of these molecular chaperones displayed ATPase activity and the ability to refold heat-inactivated luciferase in a geldanamycin- and radicicol-sensitive manner, suggesting that post-translational modifications are not involved in the modulation of Hsp90alpha activity. We show that the incubation of recombinant p53 at 37 degrees C decreases the level of its wild-type conformation and strongly inhibits the in vitro binding of p53 to the p21 promoter sequence. Interestingly, Hsp90 in an ATP-dependent manner can positively modulate p53 DNA binding after incubation at physiological temperature of 37 degrees C. Other recombinant human chaperones from Hsp70 and Hsp40 families were not able to efficiently substitute Hsp90 in this reaction. Consistent with our in vivo results, geldanamycin can suppress Hsp90 ability to regulate in vitro p53 DNA binding to the promoter sequence. In summary, the results presented in this article state that chaperone activity of Hsp90 is important for the transcriptional activity of genotypically wild-type p53.
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PMID:Hsp90 chaperones wild-type p53 tumor suppressor protein. 1535 69

The molecular chaperone Hsp90 mediates the ATP-dependent activation of a large number of proteins involved in signal transduction. During this process, Hsp90 was found to associate transiently with several accessory factors, such as p23/Sba1, Hop/Sti1, and prolyl isomerases. It has been shown that ATP hydrolysis triggers conformational changes within Hsp90, which in turn are thought to mediate conformational changes in the substrate proteins, thereby causing their activation. The specific role of the partner proteins in this process is unknown. Using proteins from Saccharomyces cerevisiae, we characterized the interaction of Hsp90 with its partner protein p23/Sba1. Our results show that the nucleotide-dependent N-terminal dimerization of Hsp90 is necessary for the binding of Sba1 to Hsp90 with an affinity in the nanomolar range. Two Sba1 molecules were found to bind per Hsp90 dimer. Sba1 binding to Hsp90 resulted in a decreased ATPase activity, presumably by trapping the hydrolysis state of Hsp90ATP. Ternary complexes of Hsp90Sba1 could be formed with the prolyl isomerase Cpr6, but not with Sti1. Based on these findings, we propose a model that correlates the ordered assembly of the Hsp90 co-chaperones with distinct steps of the ATP hydrolysis reaction during the chaperone cycle.
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PMID:The Co-chaperone Sba1 connects the ATPase reaction of Hsp90 to the progression of the chaperone cycle. 1536 69

ATP hydrolysis by the Hsp90 molecular chaperone requires a connected set of conformational switches triggered by ATP binding to the N-terminal domain in the Hsp90 dimer. Central to this is a segment of the structure, which closes like a "lid" over bound ATP, promoting N-terminal dimerization and assembly of a competent active site. Hsp90 mutants that influence these conformational switches have strong effects on ATPase activity. ATPase activity is specifically regulated by Hsp90 co-chaperones, which directly influence the conformational switches. Here we have analyzed the effect of Hsp90 mutations on binding (using isothermal titration calorimetry and difference circular dichroism) and ATPase regulation by the co-chaperones Aha1, Sti1 (Hop), and Sba1 (p23). The ability of Sti1 to bind Hsp90 and arrest its ATPase activity was not affected by any of the mutants screened. Sba1 bound in the presence of AMPPNP to wild-type and ATPase hyperactive mutants with similar affinity but only very weakly to hypoactive mutants despite their wild-type ATP affinity. Unexpectedly, in all cases Sba1 bound to Hsp90 with a 1:2 molar stoichiometry. Aha1 binding to mutants was similar to wild-type, but the -fold activation of their ATPase varied substantially between mutants. Analysis of complex formation with co-chaperone mixtures showed Aha1 and p50cdc37 able to bind Hsp90 simultaneously but without direct interaction. Sba1 and p50cdc37 bound independently to Hsp90-AMPPNP but not together. These data indicated that Sba1 and Aha1 regulate Hsp90 by influencing the conformational state of the "ATP lid" and consequent N-terminal dimerization, whereas Sti1 does not.
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PMID:Co-chaperone regulation of conformational switching in the Hsp90 ATPase cycle. 1546 38

The high-affinity ligand-binding form of unactivated steroid receptors exists as a multicomponent complex that includes heat shock protein (Hsp)90; one of the immunophilins cyclophilin 40 (CyP40), FKBP51, or FKBP52; and an additional p23 protein component. Assembly of this heterocomplex is mediated by Hsp70 in association with accessory chaperones Hsp40, Hip, and Hop. A conserved structural element incorporating a tetratricopeptide repeat (TPR) domain mediates the interaction of the immunophilins with Hsp90 by accommodating the C-terminal EEVD peptide of the chaperone through a network of electrostatic and hydrophobic interactions. TPR cochaperones recognize the EEVD structural motif common to both Hsp90 and Hsp70 through a highly conserved clamp domain. In the present study, we investigated in vitro the molecular interactions between CyP40 and FKBP52 and other stress-related components involved in steroid receptor assembly, namely Hsp70 and Hop. Using a binding protein-retention assay with CyP40 fused to glutathione S-transferase immobilized on glutathione-agarose, we have identified the constitutively expressed form of Hsp70, heat shock cognate (Hsc)70, as an additional target for CyP40. Deletion mapping studies showed the binding determinants to be similar to those for CyP40-Hsp90 interaction. Furthermore, a mutational analysis of CyP40 clamp domain residues confirmed the importance of this motif in CyP40-Hsc70 interaction. Additional residues thought to mediate binding specificity through hydrophobic interactions were also important for Hsc70 recognition. CyP40 was shown to have a preference for Hsp90 over Hsc70. Surprisingly, FKBP52 was unable to compete with CyP40 for Hsc70 binding, suggesting that FKBP52 discriminates between the TPR cochaperone-binding sites in Hsp90 and Hsp70. Hop, which contains multiple units of the TPR motif, was shown to be a direct competitor with CyP40 for Hsc70 binding. Similar to Hop, CyP40 was shown not to influence the adenosine triphosphatase activity of Hsc70. Our results suggest that CyP40 may have a modulating role in Hsc70 as well as Hsp90 cellular function.
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PMID:Interaction of the Hsp90 cochaperone cyclophilin 40 with Hsc70. 1549 3

The ATPase activity of the molecular chaperone Hsp90 is essential for its function in the assembly of client proteins. To understand the mechanism of human Hsp90, we have carried out a detailed kinetic analysis of ATP binding, hydrolysis and product release. ATP binds rapidly in a two-step process involving the formation of a diffusion-collision complex followed by a conformational change. The rate-determining step was shown to be ATP hydrolysis and not subsequent ADP dissociation. There was no evidence from any of the biophysical measurements for cooperativity in either nucleotide binding or hydrolysis for the dimeric protein. A monomeric fragment, lacking the C-terminal dimerisation domain, showed no dependence on protein concentration and, therefore, subunit association for activity. The thermodynamic linkage between client protein binding and nucleotide affinity revealed ATP bound Hsp90 has a higher affinity for client proteins than the ADP bound form. The kinetics are consistent with independent Michaelis-Menten catalysis in each subunit of the Hsp90 dimer. We propose that Hsp90 functions in an open-ring configuration for client protein activation.
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PMID:Independent ATPase activity of Hsp90 subunits creates a flexible assembly platform. 1553 47

A chimera composed of the natural products radicicol and geldanamycin has been prepared through an amide linkage connecting the resorcinol moiety of radicicol to the quinone ring of geldanamycin. The inhibitory activity of these compounds was determined by their ability to inhibit Hsp90's inherent ATPase activity along with degradation of the Hsp90 client protein, HER-2 in MCF-7 breast cancer cells. [reaction: see text]
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PMID:Design, synthesis, and evaluation of a radicicol and geldanamycin chimera, radamide. 1554 50


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