Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the cytoplasm of eukaryotes, the folding of actins and tubulins is facilitated via interaction with a heteromeric toroidal complex (cytoplasmic chaperonin). The folding reaction consists of the formation of a binary complex between the unfolded target protein and the chaperonin, followed by the ultimate release of the native polypeptide in an ATP-dependent reaction. Here we show that the mitochondrial chaperonin (cpn60) and the cytoplasmic chaperonin both recognize a range of target proteins with different relative affinities; however, the cytoplasmic chaperonin shows the highest affinity for intermediates derived from unfolded tubulins and actins. These high-affinity actin and tubulin folding intermediates are distinct from the "molten globule" intermediates formed by noncytoskeletal target proteins in that they form relatively slowly. We show that the interaction between cytoplasmic chaperonin and unfolded target proteins depends on the chaperonin being in its ADP-bound state and that the release of the target protein occurs after a transition of the chaperonin to the ATP-bound state. Our data suggest a model in which ATP hydrolysis acts as a switch between conformational forms of the cytoplasmic chaperonin that interact either strongly or weakly with unfolded substrates.
Mol Cell Biol 1994 May
PMID:Facilitated folding of actins and tubulins occurs via a nucleotide-dependent interaction between cytoplasmic chaperonin and distinctive folding intermediates. 790 54

We report the isolation and sequence of genomic clones encoding a chaperonin 60 gene from the human malaria parasite Plasmodium falciparum. The gene contains a single intron of 868 nucleotides, the largest yet identified in this organism. The reading frame encodes a product with a predicted length of 719 amino acid residues (81.6 kDa), which is considerably longer than any chaperonin 60 protein sequenced to date, revealing good identity with other chaperonin 60 proteins. There is a putative mitochondrial signal peptide and an usually long carboxy terminus composed almost entirely of glutamic and aspartic acid residues. The gene was located on chromosome 12, and a 4-kb transcript was identified.
Mol Biochem Parasitol 1994 Mar
PMID:Isolation and characterization of a chaperonin-60 gene of the human malaria parasite Plasmodium falciparum. 791 21

The purification and characterization of a new type of thermostable chaperonin from the archaebacterium Sulfolobus solfataricus is described. The chaperonin forms a hetero-oligomeric complex of two different, but closely related, subunits, which we have assigned TF55-alpha and TF55-beta. Their N-terminal sequences and amino acid residue compositions are reported. Two-dimensional projections of the chaperonin have been reconstructed from electron microscopy images, showing a 9-fold symmetrical complex, about 17.5 nm in height and 16 nm in diameter, with a central cavity of 4.5 nm. The complex is resistant to denaturing agents at room temperature and only pH values lower than 2 lead to dissociation. The separated subunits do not reassemble spontaneously but require Mg2+ and ATP for complex formation. Both subunits are necessary for formation of the TF55 oligomer. Significant structural changes have been observed after phosphorylation, thus providing evidence for a structural mobility during the chaperonin-assisted folding process of a protein. The phosphorylation reaction is modulated by potassium and magnesium ions. Magnesium seems to have an inhibitory effect, whereas potassium enhances this reaction.
J Mol Biol 1994 Sep 30
PMID:The molecular chaperonin TF55 from the Thermophilic archaeon Sulfolobus solfataricus. A biochemical and structural characterization. 793 99

Though the chaperonins that mediate folding in prokaryotes, mitochondria, and chloroplasts have been relatively well characterized, the folding of proteins in the eukaryotic cytosol is much less well understood. We recently identified a cytoplasmic chaperonin as an 800-kDa multisubunit toroid which forms a binary complex with unfolded actin; the correctly folded polypeptide is released upon incubation with Mg-ATP (Y. Gao, J. O. Thomas, R. L. Chow, G.-H. Lee, and N. J. Cowan, Cell 69:1043-1050, 1992). Here we show that the same chaperonin also forms a binary complex with unfolded alpha- or beta-tubulin; however, there is no detectable release of the correctly folded product, irrespective of the concentration of added Mg-ATP and Mg-GTP or the presence of added carrier tubulin heterodimers with which newly folded alpha- or beta-tubulin polypeptides might exchange. Rather, two additional protein cofactors are required for the generation of properly folded alpha- or beta-tubulin, which is then competent for exchange into preexisting alpha/beta-tubulin heterodimers. We show that actin and tubulins compete efficiently with one another for association with cytoplasmic chaperonin complexes. These data imply that actin and alpha- and beta-tubulin interact with the same site(s) on chaperonin complexes.
Mol Cell Biol 1993 Apr
PMID:Two cofactors and cytoplasmic chaperonin are required for the folding of alpha- and beta-tubulin. 809 61

We have created yeast strains in which the mitochondrial chaperonin, hsp60, can be either physically depleted or functionally inactivated. Cells completely depleted of hsp60 stop growing but retain for awhile the capacity to reaccumulate hsp60. While this newly made hsp60 is targeted to and processed correctly within the mitochondrion, assembly of a functional hsp60 complex does not occur. Rather, the hsp60 monomers are localized in different-size soluble complexes containing another mitochondrial chaperone, the mitochondrial form of hsp70. A number of other mitochondrial matrix-targeted proteins synthesized in the absence of functional hsp60 are imported into mitochondria but often show some buildup of precursor forms and, unlike hsp60, accumulate as insoluble aggregates. By contrast, several mitochondrial proteins normally targeted to the intermembrane space show normal processing in the complete absence of a functional hsp60 complex. Similar and complementary results were obtained when we examined the metabolism of matrix- and intermembrane space-localized proteins in cells expressing three different temperature-sensitive alleles of HSP60. In all cases, matrix-targeted proteins synthesized at nonpermissive (i.e., hsp60-inactivating) temperatures were correctly targeted to and processed within mitochondria but accumulated predominantly or totally as insoluble aggregates. The metabolism of two intermembrane space proteins, cytochrome b2 and cytochrome c1, was unaffected at the nonpermissive temperature, as judged by the correct processing and complete solubility of newly synthesized forms of both proteins. These findings are discussed with regard to current models of intermembrane targeting.
Mol Cell Biol 1993 May
PMID:Loss of mitochondrial hsp60 function: nonequivalent effects on matrix-targeted and intermembrane-targeted proteins. 809 78

In this study we present evidence indicating that GroE chaperonins mediate de novo protein folding of heterodimeric and monomeric luciferases under heat shock or sub-heat shock conditions in vivo. The effects of additional groESL and groEL genes on the bioluminescence of Escherichia coli cells expressing different bacterial luciferase genes at various temperatures were directly studied in cells growing in liquid culture. Data indicate that at 42 degrees C GroESL chaperonins are required for the folding of the beta subunit polypeptide of the heterodimeric alpha beta luciferase from the mesophilic bacterium Vibrio harveyi MAV (B392). In contrast, the small number of amino acid substitutions present in the luciferase beta subunit polypeptide from the thermotolerant V. harveyi CTP5 suppresses this requirement for GroE chaperonins, and greatly reduces interaction between the beta subunit polypeptide and GroEL chaperonin. In addition, GroESL are required for the de novo folding at 37 degrees C of a MAV alpha beta luciferase fusion polypeptide that is functional as a monomer. No such requirement for luciferase activity is observed at that temperature with a fusion of the CTP5 alpha and beta subunit polypeptides, although GroE chaperonins can still mediate folding of the CTP5 fusion luciferase. Bacterial luciferases provide a unique system for direct observation of the effects of GroE chaperonins on protein folding and enzyme assembly in living cells. Furthermore, they offer a sensitive and simple assay system for the identification of polypeptide domains required for GroEL protein binding.
Mol Gen Genet 1993 Apr
PMID:GroE-mediated folding of bacterial luciferases in vivo. 809 58

The coding region for the Escherichia coli groEL (chaperonin-60) polypeptide was fused downstream of a pea rubisco small subunit transit peptide coding sequence under the control of a tandem 35S CaMV promoter. Transgenic tobacco plants (Nicotiana tabacum cv. Xanthi) containing this modified groEL gene were produced. The modified groEL polypeptide was correctly imported into chloroplasts and accumulated to high or low levels in different plants. The majority of the modified groEL polypeptide was processed correctly to the mature form within the chloroplasts. Approximately 20% of the imported polypeptides retained a portion of the N-terminal transit peptide (TPgroEL). Both groEL and TPgroEL polypeptides assembled into tetradecameric species in the chloroplasts. In plants accumulating high levels of these products, the majority of the plant chaperonin-60 polypeptides in the chloroplast were present in novel hybrid tetradecameric species containing both bacterial and plant chaperonin-60 polypeptides. In plants accumulating low levels of groEL, the predominant species present appeared to be authentic plant cpn60(14) and authentic bacterial groEL14. The growth and development of transgenic and control tobacco plants were indistinguishable.
Plant Mol Biol 1993 Sep
PMID:A modified Escherichia coli chaperonin (groEL) polypeptide synthesized in tobacco and targeted to the chloroplasts. 810 28

The possibilities of independent function of the two chaperonin 10 (cpn10) domains of the cpn10 homologue from spinach chloroplasts and the role of five conserved amino acid residues in the N-terminal cpn10 unit were investigated. Recombinant single domain proteins and complete chloroplast cpn10 proteins carrying amino acid exchanges of conserved residues in their N-terminal cpn10 domain were expressed in Escherichia coli and partially purified. The function of the recombinant proteins was tested using GroEL as chaperonin 60 (cpn60) partner for in vitro refolding of denatured ribulose-1,5-bisphosphate carboxylase (Rubisco). Interaction with cpn60 was also monitored by the ability to inhibit GroEL ATPase activity. In vitro both isolated cpn10 domains were found to be incapable of co-chaperonin function. All mutants were also severely impaired in cpn10 function. The results are interpreted in terms of an essential role of the exchanged amino acid residues for the interaction between co-chaperonin and cpn60 partner and in terms of a functional coupling of both cpn10 domains. To test the function of mutant chloroplast cpn10 proteins in vivo the cpn10 deficiency of E. coli strain CG712 resulting in an inability to assemble lambda-phage was exploited in a complementation assay. Transformation with plasmids directing the expression of mutant chloroplas cpn10 proteins in two cases restored lambda-phage assembly in this bacterial strain to the same extent as did transformation with a plasmid encoding wild-type cpn10 protein. In contrast a plasmid encoded third mutant and truncated forms of chloroplast cpn10 showed significantly reduced complementation efficiencies.
Plant Mol Biol 1995 Dec
PMID:Functional analysis of isolated cpn10 domains and conserved amino acid residues in spinach chloroplast co-chaperonin by site-directed mutagenesis. 855 47

An RNA-binding activity has been identified in Escherichia coli that provides physical protection of RNA against ribonucleases in an ATP- and Mg(2+)-dependent manner. This binding activity is stimulated under growth conditions known to cause a decrease in the rate of mRNA decay. RNA protection is mediated by a protein complex that contains a modified form of the chaperonin GroEL as an indispensable constituent. These results suggest a new role for GroEL as an RNA chaperone.
Mol Microbiol 1995 Jun
PMID:Identification of GroEL as a constituent of an mRNA-protection complex in Escherichia coli. 857 58

The crystal structures of the chaperonin GroEL Arg13 --> Gly; Ala126 --> Val double mutant, without and in complex with ATP gamma S, have been determined at atomic resolution. Here, we show that the double mutation Arg13 --> Gly; Ala126 --> Val disrupts negative co-operativity between GroEL rings, with respect to ATP, but has little effect on the positive co-operativity within each ring. Our results help to explain why the double mutation facilitated the crystallization of GroEL and why breaking of dyad symmetry between rings is not observed in crystal structures of this mutant. Our results may also help to explain why the observed structural differences between the GroEL double mutant and its ATP gamma S-bound form are small.
J Mol Biol 1996 May 24
PMID:Inter-ring communication is disrupted in the GroEL mutant Arg13 --> Gly; Ala126 --> Val with known crystal structure. 863 5


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>