[Dynamic conformational changes which support the function of molecular chaperone GroE].
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Adenosine Triphosphate↗
Biomedical subjects
T Mizobata
Publications and source records attributed to T Mizobata.
Refolding of target proteins from a "rigid" mutant chaperonin demonstrates a minimal mechanism of chaperonin binding and release.
One of the most interesting facets of GroEL-facilitated protein folding lies in the fact that the requirement for a successful folding reaction of a given protein target depends upon the refolding conditions used. In this report, we utilize a mutant of GroEL (GroEL T89W) whose domain movements have been drastically restricted, producing a chaperonin that is incapable of utilizing the conventional cyclic mechanism of chaperonin action. This mutant was, however, still capable of improving the refolding yield of lactate dehydrogenase in the absence of both GroES and ATP hydrolysis. A very rapid interconversion of conformations was detected in the mutant immediately after ATP binding, and this interconversion was inferred to form part of the target release mechanism in this mutant. The possibility exists that some target proteins, although dependent on GroEL for improved refolding yields, are capable of refolding successfully by utilizing only portions of the entire mechanism provided by the chaperonins.
Adenosine Triphosphate↗
Overproduction of Thermus sp. YS 8-13 manganese catalase in Escherichia coli production of soluble apoenzyme and in vitro formation of active holoenzyme.
Overproduction of Thermus sp. YS 8-13 manganese catalase in Escherichia coli BL21(DE3) was accomplished by introducing a derivative of pET-23a(+) containing a copy of the coding gene into the multicloning site. E. coli BL21(DE3)/pETMNCAT produced abundant quantities of manganese catalase as insoluble inclusion bodies. Regeneration of active catalase was achieved by denaturation in guanidine hydrochloride and subsequent dialysis in the presence of manganese ion. When the E. coli chaperone genes GroEL, GroES, DnaK, DnaJ and GrpE were coexpressed with manganese catalase, a significant fraction of the overproduced protein was partitioned into the soluble fraction. However, almost all of the soluble enzyme was isolated in a manganese-deficient apo form which could subsequently be converted into active holoenzyme by incubation with manganese ion at high temperatures. Further experiments on this apo catalase suggested that the structure of this protein was virtually identical to the active holoenzyme.
Apoenzymes↗
Cloning and over-expression of thermostable Bacillus sp. YM55-1 aspartase and site-directed mutagenesis for probing a catalytic residue.
A thermostable aspartase gene (aspB) from Bacillus sp. YM55-1 was cloned and the gene sequenced. The aspB gene (1407 bp ORF) encodes a protein with a molecular mass of 51 627 Da, consisting of 468 amino-acid residues. An amino-acid sequence comparison revealed that Bacillus YM55-1 aspartase shared 71% homology with Bacillus subtilis aspartase and 49% with Escherichia coli and Pseudomonas fluorescens aspartases. The E. coli TK237/pUCASPB strain, which was obtained by transforming E. coli TK237 (aspartase-null strain) with a vector plasmid (pUCASPB) containing the cloned aspB gene, produced a large amount of the enzyme corresponding to > 10% of the total soluble protein. The over-expressed recombinant enzyme (native molecular mass: 200 kDa) was purified effectively and rapidly using heat treatment and affinity chromatography. In order to probe the catalytic residues of this enzyme, two conserved amino-acid residues, Lys183 and His134, were individually mutated to alanine. Although the tertiary structure of each mutant was estimated to be the same as that of wild-type aspartase in CD and fluorescence measurements, the Lys183Ala mutant lost its activity completely, whereas His134Ala retained full activity. This finding suggests that Lys183 may be involved in the catalytic activity of this thermostable Bacillus YM55-1 aspartase.
Amino Acid Sequence↗
[A novel adult case of acute necrotizing encephalopathy of childhood with bilateral symmetric thalamic lesions].
This report describes a 46-year-old Japanese woman with bilateral symmetric thalamic necrosis. The unusual radiologic findings are discussed in relation with acute necrotizing encephalopathy (ANE) of childhood, a rare disease proposed by Mizuguchi et al. ANE affects young children and the incidence is highest between 6 and 18 months of ages. There is only one report of an adult case. The acute stage pathology in ANE can be summarized as acute edema and necrosis involving both gray and white matter by local breakdown of the blood-brain barrier. The radiologic findings in our case were similar to those in ANE of childhood. Though the pathogenesis between our adult case and ANE of childhood might be different, severe hypoalbuminea in our case could cause the alteration of permeability of the thalamic vessels, which might accelerate breakdown of the blood-brain barrier in the thalamus.
Albumins↗
Functional communications between the apical and equatorial domains of GroEL through the intermediate domain.
The Escherichia coli GroEL subunit consists of three domains with distinct functional roles. To understand the role of each of the three domains, the effects of mutating a single residue in each domain (Y203C at the apical, T89W at the equatorial, and C138W at the intermediate domain) were studied in detail, using three different enzymes (enolase, lactate dehydrogenase, and rhodanese) as refolding substrates. By analyzing the effects of each mutation, a transfer of signals was detected between the apical domain and the equatorial domain. A signal initiated by the equatorial domain triggers the release of polypeptide from the apical domain. This trigger was independent of nucleotide hydrolysis, as demonstrated using an ATPase-deficient mutant, and, also, the conditions for successful release of polypeptide could be modified by a mutation in the apical domain, suggesting that the polypeptide release mechanism of GroEL is governed by chaperonin-target affinities. Interestingly, a reciprocal signal from the apical domain was suggested to occur, which triggered nucleotide hydrolysis in the equatorial domain. This signal was disrupted by a mutation in the intermediate domain to create a novel ternary complex in which GroES and refolding protein are simultaneously bound in a stable ternary complex devoid of ATPase activity. These results point to a multitude of signals which govern the overall chaperonin mechanism.
Adenosine Triphosphate↗
Unfolding and refolding of Escherichia coli chaperonin GroES is expressed by a three-state model.
The guanidine-hydrochloride (Gdn-HCl) induced unfolding and refolding characteristics of the co-chaperonin GroES from Escherichia coli, a homoheptamer of subunit molecular mass 10,000 Da, were studied by using intrinsic fluorescence, 1-anilino-8-naphthalene sulfonate (ANS) binding, and size-exclusion HPLC. When monitored by tyrosine fluorescence, the unfolding reaction of GroES consisted of a single transition, with a transition midpoint at around 1.0 M Gdn-HCl. Interestingly, however, ANS binding and size-exclusion HPLC experiments strongly suggested the existence of an intermediate state in the transition. In order to confirm the existence of an intermediate state between the native heptameric and unfolded monomeric states, a tryptophan residue was introduced into the interface of GroES subunits as a fluorescent probe. The unfolding reaction of GroES I48W as monitored by tryptophyl fluorescence showed a single transition curve with a transition midpoint at 0.5 M Gdn-HCl. This unfolding transition curve as well as the refolding kinetics were dependent on the concentration of GroES protein. CD spectrum and size-exclusion HPLC experiments demonstrated that the intermediates assumed a partially folded conformation at around 0.5 M Gdn-HCl. The refolding of GroES protein from 3 M Gdn-HCl was probed functionally by measuring the extent of inhibition of GroEL ATPase activity and the enhancement of lactate dehydrogenase refolding yields in the presence of GroEL and ADP. These results clearly demonstrated that the GroES heptamer first dissociated to monomers and then unfolded completely upon increasing the concentration of Gdn-HCl, and that both transitions were reversible. From the thermodynamic analysis of the dissociation reaction, it was found that the partially folded monomer was only marginally stable and that the stability of GroES protein is governed mostly by the association of the subunits.
Chaperonin 10↗
Purification and characterization of thermostable aspartase from Bacillus sp. YM55-1.
A thermostable aspartase was purified from a thermophile Bacillus sp. YM55-1 and characterized in terms of activity and stability. The enzyme was isolated by a 5-min heat treatment at 75 degrees C in the presence of 11% (w/v) ammonium sulfate and 100 mM aspartate, followed by Q-Sepharose anion-exchange and AF-Red Toyopearl chromatographies. The native molecular weight of aspartase determined by gel filtration was about 200,000, and this enzyme was composed of four identical monomers with molecular weights of 51,000 determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Unlike Escherichia coli aspartase, the enzyme was not activated by the presence of magnesium ion at alkaline pH. At the optimum pH, the Km and Vmax were 28.5 mM and 700 units/mg at 30 degrees C and 32.0 mM and 2200 units/mg at 55 degrees C, respectively. The specific activity was four and three times higher than those of E. coli and Pseudomonas fluorescens enzymes at 30 degrees C, respectively. Eighty percent of the activity was retained after a 60-min incubation at 55 degrees C, and the enzyme was also resistant to chemical denaturants; 80% of the initial specific activity was detected in assay mixtures containing 1.0 M guanidine hydrochloride. The purified enzyme shared a high sequence homology in the N-terminal region with aspartases from other organisms.
Amino Acid Sequence↗
Purification and cloning of a thermostable manganese catalase from a thermophilic bacterium.
We have purified a heat-stable catalase from a thermophilic bacterium, Thermus species strain YS 8-13. The enzyme was purified 160-fold from crude cellular extracts and possessed a specific activity of 8000 units/mg at 65 degrees C. The purified enzyme displayed the highest activity at pH 7 to 10 and temperatures around 85 degrees C. The catalase was determined to be a manganese catalase, based on results from atomic absorption spectra and inhibition experiments using sodium azide. The enzyme was composed of six identical subunits of molecular weight 36,000. Amino acid sequences determined from the purified protein were used to design oligonucleotide primers, which were in turn used to clone the coding gene. The nucleotide sequence of a 1.4-kb fragment of Thermus sp. YS 8-13 genomic DNA containing a 909-bp open reading frame was determined. The gene encoded a 302-residue polypeptide of deduced molecular weight 33,303. The deduced amino acid sequence displayed a region-specific homology with the sequences of the manganese catalase from a mesophilic organism, Lactobacillus plantarum.
Amino Acid Sequence↗
Functional magnetic resonance imaging to word generation task in a patient with Broca's aphasia.
We describe the findings of functional magnetic resonance imaging (fMRI) in a patient with Broca's aphasia. The patient was a 45-year-old, right-handed woman who developed Broca's aphasia after infarction in the left frontal lobe. The first fMRI showed no signals in the left frontal lobe during verbal tasks, 2 weeks after the onset of infarction. Four weeks later, when the patient's symptom had improved, the second fMRI showed some increase in the fMRI signals in the left frontal lobe. Seven months later, she had completely recovered the ability to speak. The last fMRI then showed that the increment in signal activity in the left frontal lobe during verbal tasks had recovered to the level seen in normal subjects. There was a good correlation between the increase in task-related signals in Broca's area and the recovery of language function. Our findings show that fMRI has can be important in assessing cognitive functions in patients with Broca's aphasia.
Aphasia, Broca↗
Endothelins stimulate expression of cyclooxygenase 2 in rat cultured astrocytes.
Endothelin (ET) is one of the active endogenous substances regulating the functions of astrocytes. In the present study, we examined effects of ET on cyclooxygenase (COX) expression in cultured astrocytes. ET-3 (100 nM) caused transient increases in the expression of both COX2 mRNA and protein, but not those of COX1, in cultured astrocytes. ET-induced COX2 mRNA expression was suppressed by 5 microg/ml actinomycin D, 30 microM BAPTA/AM, inhibitors of protein kinase C (1-100 nM staurosporin and 100 microM H-7), 2 microM dexamethasone, and prolonged treatment with 100 nM phorbol 12-myristate 13-acetate. ET-3 stimulated production of prostaglandin (PG) E2 in cultured astrocytes. The effect of ET-3 on the PGE2 production was diminished by actinomycin D. Indomethacin and NS398, a selective COX2 inhibitor, comparably decreased both the basal and the ET-stimulated PGE2 production. Proliferation of cultured astrocytes was stimulated by 100 nM ET-3, and the increased proliferation was reduced by co-addition of 1 microM PGE2. Treatment with 1 microM PGE2 caused astrocytic morphological changes accompanied by disappearance of stress fibers, a prominent structure of organized cytoskeletal actin in cultured astrocytes. In the presence of 10 nM ET-3, PGE2 did not show an effect on astrocytic actin organization. The present study shows that ET is an inducer of astrocytic COX2 and suggests that ET-induced PGE2 production through COX2 may be involved in the regulation of astrocytic functions.
Animals↗
Purification and characterization of a thermostable class II fumarase from Thermus thermophilus.
A thermostable fumarase was purified from a strain of Thermus thermophilus isolated from a Japanese hot spring. The maximum specific activity of the purified enzyme was 1740 units/mg at pH 8.0 and 85 degreesC. The enzyme was composed of four identical subunits with a molecular weight of 46,000 and displayed other enzymatic characteristics which are common to the class II fumarases. The thermal stability of the purified enzyme was remarkable, with over 80% of the activity remaining after a 24-h incubation at 90 degreesC. The enzyme was also resistant to chemical denaturants; 50% of the initial specific activity was detected in assay mixtures containing 0.8 M guanidine hydrochloride. The purified enzyme shared an extremely high sequence homology with Thermus aquaticus fumarase and Bacillus subtilis fumarase in the first 43 amino acid residues.
Amino Acid Sequence↗
Chaperonin GroE-facilitated refolding of disulfide-bonded and reduced Taka-amylase A from Aspergillus oryzae.
The refolding characteristics of Taka-amylase A (TAA) from Aspergillus oryzae in the presence of the chaperonin GroE were studied in terms of activity and fluorescence. Disulfide-bonded (intact) TAA and non-disulfide-bonded (reduced) TAA were unfolded in guanidine hydrochloride and refolded by dilution into buffer containing GroE. The intermediates of both intact and reduced enzymes were trapped by GroEL in the absence of nucleotide. Upon addition of nucleotides such as ATP, ADP, CTP or UTP, the intermediates were released from GroEL and recovery of activity was detected. In both cases, the refolding yields in the presence of GroEL and ATP were higher than spontaneous recoveries. Fluorescence studies of intrinsic tryptophan and a hydrophobic probe, 8-anilinonaphthalene-1-sulfonate, suggested that the intermediates trapped by GroEL assumed conformations with different hydrophobic properties. The presence of protein disulfide isomerase or reduced and oxidized forms of glutathione in addition to GroE greatly enhanced the refolding reaction of reduced TAA. These findings suggest that GroE has an ability to recognize folding intermediates of TAA protein and facilitate refolding, regardless of the existence or absence of disulfide bonds in the protein.
Adenosine Triphosphate↗
Purification and characterization of chaperonins 60 and 10 from Methylobacillus glycogenes.
Two proteins belonging to the group I chaperonin family were isolated from an obligate methanotroph, Methylobacillus glycogenes. The two proteins, one a GroEL homologue (cpn60: M. glycogenes 60 kDa chaperonin) and the other a GroES homologue (cpn10: M. glycogenes 10 kDa chaperonin), composed a heteropolymeric complex in the presence of ATP. Both proteins were purified from crude extracts of M. glycogenes by anion-exchange (DEAE-Toyopearl) and gel-filtration (Sephacryl S-400) chromatography. The native molecular weights of each chaperonin protein as determined by high-performance liquid chromatography (HPLC) gel-filtration were 820 000 for cpn60 and 65 000 for cpn10. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the subunit molecular weights of cpn60 and cpn10 were 58 000 and 10 000, respectively. Both cpn60 and cpn10 possessed amino acid sequences which were highly homologous to other group I chaperonins. M. glycogenes cpn60 displayed an ATPase activity which was inhibited in the presence of cpn10. The chaperonins also displayed an ability to interact with and facilitate the refolding of Thermus malate dehydrogenase and yeast enolase in a manner similar to that of GroEL/ES. The similarities between the Escherichia coli GroE proteins are discussed.
Adenosine Triphosphatases↗
The role of ATP hydrolysis in the function of the chaperonin GroEL: dynamic complex formation with GroES.
In order to understand the role of ATP hydrolysis of the chaperonin GroEL during protein folding, we have studied GroEL-GroES complex formation in the presence of ATP or ADP by using capillary electrophoresis and surface plasmon resonance. Capillary electrophoresis analysis showed that the GroEL 14-mer and GroES 7-mer formed a 1:1 complex in the presence of ATP. In the presence of ADP, both the association and dissociation rates of the complex were slower by about one order of magnitude than the rates in the presence of ATP at 25 degrees C. The implications of such a stable complex on the overall mechanism of chaperonin function are discussed.
Adenosine Diphosphate↗
The folding characteristics of tryptophanase from Escherichia coli.
The unfolding and refolding characteristics of Escherichia coli tryptophanase (tryptophan indole-lyase) [EC 4.1.99.1] in guanidine hydrochloride were studied. Tryptophanase unfolded by first dissociating its coenzyme, pyridoxal 5'-phosphate, from the active site. This dissociation caused a significant destabilization of structure, and global unfolding of the protein followed. During this global unfolding step, an intermediate was formed which had a strong tendency to aggregate irreversibly, as detected by light scattering experiments. Tryptophanase was unable to refold quantitatively after unfolding in 4 M guanidine hydrochloride. The low refolding yield was due to non-specific aggregation which occurs during refolding. Various conditions which limited this aggregation were probed, and it was found that by initiating the refolding reaction at low temperature, the aggregation of tryptophanase folding intermediates during the reaction could be avoided to a certain extent, and the refolding yield improved.
Apoenzymes↗
The guanidine-induced conformational changes of the chaperonin GroEL from Escherichia coli. Evidence for the existence of an unfolding intermediate state.
Equilibrium unfolding experiments of the E. coli chaperonin GroEL were performed in guanidine hydrochloride. A reversible unfolding intermediate was observed in very low concentrations of denaturant (< 0.5 M guanidine hydrochloride). This intermediate was characterized by a decreased light scattering intensity and an increased binding of the fluorescent probe 1-anilino-8-naphthalene sulfonate. No significant changes in circular dichroism spectra were observed for this unfolding intermediate. A second decrease in fluorescence intensity and light scattering was observed in higher concentrations of guanidine hydrochloride, with a transitional midpoint of 1.15 M. This transition was accompanied by the complete loss of secondary structure, as monitored by circular dichroism spectroscopy. This second transition agreed well with the results previously reported in this journal (Price et al. (1993) Biochim. Biophys. Acta 1161, 52-58).
Chaperonin 60↗
Chaperonin GroE and ADP facilitate the folding of various proteins and protect against heat inactivation.
In the presence of ADP, the molecular chaperones GroEL and GroES from Escherichia coli not only facilitated the refolding of various proteins, but also prevented their irreversible heat inactivation in vitro. Without nucleotides the refolding reactions were arrested by GroEL. Addition of GroES and ADP to the reaction mixture initiated the refolding reactions and the enzyme activities were regained efficiently. The presence of GroE (GroEL and GroES) and ADP also protected against heat inactivation of native enzymes at various temperatures. These findings suggest that in the presence of GroES, nucleotide binding is an important event in the mechanism of GroEL-facilitated protein folding.
Adenosine Diphosphate↗