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Evolution of enzymatic activity in the enolase superfamily: structural and mutagenic studies of the mechanism of the reaction catalyzed by o-succinylbenzoate synthase from Escherichia coli.

o-Succinylbenzoate synthase (OSBS) from Escherichia coli, a member of the enolase superfamily, catalyzes an exergonic dehydration reaction in the menaquinone biosynthetic pathway in which 2-succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylate (SHCHC) is converted to 4-(2'-carboxyphenyl)-4-oxobutyrate (o-succinylbenzoate or OSB). Our previous structural studies of the Mg(2+).OSB complex established that OSBS is a member of the muconate lactonizing enzyme subgroup of the superfamily: the essential Mg(2+) is coordinated to carboxylate ligands at the ends of the third, fourth, and fifth beta-strands of the (beta/alpha)(7)beta-barrel catalytic domain, and the OSB product is located between the Lys 133 at the end of the second beta-strand and the Lys 235 at the end of the sixth beta-strand [Thompson, T. B., Garrett, J. B., Taylor, E. A, Meganathan, R., Gerlt, J. A., and Rayment, I. (2000) Biochemistry 39, 10662-76]. Both Lys 133 and Lys 235 were separately replaced with Ala, Ser, and Arg residues; all six mutants displayed no detectable catalytic activity. The structure of the Mg(2+).SHCHC complex of the K133R mutant has been solved at 1.62 A resolution by molecular replacement starting from the structure of the Mg(2+).OSB complex. This establishes the absolute configuration of SHCHC: the C1-carboxylate and the C6-OH leaving group are in a trans orientation, requiring that the dehydration proceed via a syn stereochemical course. The side chain of Arg 133 is pointed out of the active site so that it cannot function as a general base, whereas in the wild-type enzyme complexed with Mg(2+).OSB, the side chain of Lys 133 is appropriately positioned to function as the only acid/base catalyst in the syn dehydration. The epsilon-ammonium group of Lys 235 forms a cation-pi interaction with the cyclohexadienyl moiety of SHCHC, suggesting that Lys 235 also stabilizes the enediolate anion intermediate in the syn dehydration via a similar interaction.

Amino Acid Substitution↗

Evolutionary potential of (beta/alpha)8-barrels: in vitro enhancement of a "new" reaction in the enolase superfamily.

The repertoire of reactions in the mechanistically diverse enolase superfamily is the result of divergent evolution that conserved enolization of a carboxylate anion substrate but allowed different overall reactions using different substrates. Details of the pathways for the natural evolutionary process are unknown, but the events reasonably involve (1) incremental increases in the level of the "new" reaction that would provide a selective advantage and (2) an accompanying loss of the "old" reaction catalyzed by the progenitor. In an effort to better understand the molecular processes of divergent evolution, the D297G mutant of the l-Ala-d/l-Glu epimerase (AEE) from Escherichia coli was designed so that it could bind the substrate for the o-succinylbenzoate synthase (OSBS) reaction and, as a result, catalyze that reaction [Schmidt, D. M. Z., Mundorff, E. C., Dojka, M., Bermudez, E., Ness, J. E., Govindarajan, S., Babbitt, P. C., Minshull, J., and Gerlt, J. A. (2003) Biochemistry 42, 8387-8393]. The AEE progenitor did not catalyze the OSBS reaction, but the D297G mutant catalyzed a low level of the OSBS reaction (k(cat), 0.013 s(-)(1); K(m), 1.8 mM; k(cat)/K(m), 7.4 M(-)(1) s(-)(1)) that was sufficient to permit anaerobic growth by an OSBS-deficient strain of E. coli; the level of the progenitor's natural AEE reaction was significantly diminished. Using random mutagenesis and an anaerobic metabolic selection, we now have identified the I19F substitution as an additional mutation that enhances both growth of the OSBS-deficient strain and the kinetic constants for the OSBS reaction (k(cat), 0.031 s(-)(1); K(m), 0.34 mM; k(cat)/K(m), 90 M(-)(1) s(-)(1)). Several other substitutions for Ile 19 also enhanced the level of the OSBS reaction. All of the substitutions substantially decreased the level of the AEE reaction from that possessed by the D297G progenitor. The changes in the kinetic constants for both the OSBS and AEE reactions are attributed to a readjustment of substrate specificity so that the substrate for the OSBS reaction is more productively presented to the conserved acid/base catalysts in the active site. These observations support our hypothesis that evolution of "new" functions in the enolase superfamily can occur simply by changes in specificity-determining residues.

Amino Acid Isomerases↗

Murine muscle-specific enolase: cDNA cloning, sequence, and developmental expression.

In vertebrates, the glycolytic enzyme enolase (EC 4.2.1.11) is present as homodimers and heterodimers formed from three distinct subunits of identical molecular weight, alpha, beta, and gamma. We report the cloning and sequencing of a cDNA encoding the beta subunit of murine muscle-specific enolase. The corresponding amino acid sequence shows greater than 80% homology with the beta subunit from chicken obtained by protein sequencing and with alpha and gamma subunits from rat and mouse deduced from cloned cDNAs. In contrast, there is no homology between the 3' untranslated regions of mouse alpha, beta, and gamma enolase mRNAs, which also differ greatly in length. The short 3' untranslated region of beta enolase mRNA accounts for its distinct length, 1600 bases. It is known that a progressive transition from alpha alpha to beta beta enolase occurs in developing skeletal muscle. We show that this transition mainly results from a differential regulation of alpha and beta mRNA levels. Analysis of myogenic cell lines shows that beta enolase gene is expressed at the myoblast stage. Moreover, transfection of premyogenic C3H10T1/2 cells with MyoD1 cDNA shows that the initial expression of beta transcripts occurs during the very first steps of the myogenic pathway, suggesting that it could be a marker event of myogenic lineage determination.

Actins↗

Rapid discovery of putative protein biomarkers of traumatic brain injury by SDS-PAGE-capillary liquid chromatography-tandem mass spectrometry.

We report the rapid discovery of putative protein biomarkers of traumatic brain injury (TBI) by SDS-PAGE-capillary liquid chromatography-tandem mass spectrometry (SDS-PAGE-Capillary LC-MS(2)). Ipsilateral hippocampus (IH) samples were collected from naive rats and rats subjected to controlled cortical impact (a rodent model of TBI). Protein database searching with 15,558 uninterpreted MS(2) spectra, collected in 3 days via data-dependent capillary LC-MS(2) of pooled cyanine dye-labeled samples separated by SDS-PAGE, identified more than 306 unique proteins. Differential proteomic analysis revealed differences in protein sequence coverage for 170 mammalian proteins (57 in naive only, 74 in injured only, and 39 of 64 in both), suggesting these are putative biomarkers of TBI. Confidence in our results was obtained by the presence of several known biomarkers of TBI (including alphaII-spectrin, brain creatine kinase, and neuron-specific enolase) in our data set. These results show that SDS-PAGE prior to in vitro proteolysis and capillary LC-MS(2) is a promising strategy for the rapid discovery of putative protein biomarkers associated with a specific physiological state (i.e., TBI) without a priori knowledge of the molecules involved.

Amino Acid Sequence↗

Voltage-gated K+ current: a marker for apoptosis in differentiating neuronal progenitor cells?

We investigated apoptosis during early stages of in vitro differentiation of neuronal precursors generated by embryonic day 14 (E14) mouse striata stem cells. Differentiation was in conditions of suboptimal growth factor supply. Apoptosis reached 10-15% of cells and affected proliferating as well as postmitotic cells, including TUJ1-positive cells. Inhibition of apoptosis led to an increased proportion of TUJ1-positive cells generated by stem cells. K(+) current was reported to be related to apoptosis. Outward K(+) currents were present in differentiating neuronal precursors that were consistent with delayed rectifier and transient A-type currents. The amplitude of the delayed rectifier current varied during the first 4 days of stem cell differentiation. Current amplitude was greatly increased in the presence of staurosporine but reduced at elevated extracellular K(+) concentration. In addition, the amplitude of the current was significantly diminished by inhibiting several caspases, but not caspase 8. In Bax knock-out transgenic neuronal precursors, K(+) current was not decreased after the first day but at later stages of cell differentiation. At this early stage, apoptosis of proliferating cells and of TUJ1-positive cells was not reduced by the absence of Bax, but was by caspase 9 inhibition. Thus, activation of a delayed rectifier K(+) current in differentiating stem cells is related to apoptosis. Recordings of this current revealed that apoptosis at early stages of neuronal differentiation occurred in two phases that did not exhibit similar dependence on the proapoptotic protein Bax and that probably used different pathways.

Amino Acid Chloromethyl Ketones↗

Yeast protein glycation in vivo by methylglyoxal. Molecular modification of glycolytic enzymes and heat shock proteins.

Protein glycation by methylglyoxal is a nonenzymatic post-translational modification whereby arginine and lysine side chains form a chemically heterogeneous group of advanced glycation end-products. Methylglyoxal-derived advanced glycation end-products are involved in pathologies such as diabetes and neurodegenerative diseases of the amyloid type. As methylglyoxal is produced nonenzymatically from dihydroxyacetone phosphate and d-glyceraldehyde 3-phosphate during glycolysis, its formation occurs in all living cells. Understanding methylglyoxal glycation in model systems will provide important clues regarding glycation prevention in higher organisms in the context of widespread human diseases. Using Saccharomyces cerevisiae cells with different glycation phenotypes and MALDI-TOF peptide mass fingerprints, we identified enolase 2 as the primary methylglyoxal glycation target in yeast. Two other glycolytic enzymes are also glycated, aldolase and phosphoglycerate mutase. Despite enolase's activity loss, in a glycation-dependent way, glycolytic flux and glycerol production remained unchanged. None of these enzymes has any effect on glycolytic flux, as evaluated by sensitivity analysis, showing that yeast glycolysis is a very robust metabolic pathway. Three heat shock proteins are also glycated, Hsp71/72 and Hsp26. For all glycated proteins, the nature and molecular location of some advanced glycation end-products were determined by MALDI-TOF. Yeast cells experienced selective pressure towards efficient use of d-glucose, with high methylglyoxal formation as a side effect. Glycation is a fact of life for these cells, and some glycolytic enzymes could be deployed to contain methylglyoxal that evades its enzymatic catabolism. Heat shock proteins may be involved in proteolytic processing (Hsp71/72) or protein salvaging (Hsp26).

Amino Acid Sequence↗

Physiological characterization of a heme-deficient mutant of Staphylococcus aureus by a proteomic approach.

The high-resolution two-dimensional (2D) protein gel electrophoresis technique combined with matrix-assisted laser desorption ionization-time of flight mass spectrometry was used for identification of proteins whose levels were changed by a mutation in hemB. Cytoplasmic protein extracts obtained from the mutant and the wild type (strain COL) at different stages of growth in tryptone soya broth (exponential, transitional, and stationary growth phases) were separated on 2D protein gels. Comparison of the 2D patterns of the protein extracts of the two strains revealed major differences. Because the electron transport chain of the mutant is interrupted due to the deficiency of heme, this organism should be unable to use oxygen or nitrate as a terminal electron acceptor. Consistent with this hypothesis, proteins involved in the glycolytic pathway and related pathways (glyceraldehyde-3-phosphate dehydrogenase, enolase, and phosphoglycerate kinase) and in fermentation pathways (lactate dehydrogenase, alcohol dehydrogenase, and pyruvate formate lyase) were induced in exponentially growing cells of the mutant. These results strongly indicate that the hemB mutant generates ATP from glucose or fructose only by substrate phosphorylation. Analyses of the fermentation reactions showed that the main product was lactate. Although pyruvate formate lyase (Pfl) and pyruvate dehydrogenase were present, neither ethanol nor acetate was detected in significant amounts. Presumably, Pfl was not activated in the presence of oxygen, and pyruvate dehydrogenase might have very low activity. Transcriptional analysis of citB, encoding the aconitase, revealed that the activity of the citrate cycle enzymes was down-regulated in the hemB mutant. The arginine deiminase pathway was also induced, and it could provide ATP as well. Furthermore, the amounts of most of the extracellular virulence factors were significantly reduced by a mutation in hemB, which is consistent with previous reports.

Acetyltransferases↗

Nitrinergic and peptidergic innervation of the human oesophagus.

The distribution, colocalisation, and interconnections of nitrinergic and peptidergic neurons and nerves in the human oesophagus were examined. Cryosections of surgically resected tissues from eight subjects were studied with indirect immunofluorescence for the presence of 11 neuropeptides and neuron specific enolase. After immunohistochemistry, nitric oxide synthase was shown on the same sections with the beta nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemical reaction. The histochemical findings were verified immunohistochemically on other sections with an antiserum against nitric oxide synthase. Most myenteric neurons (55%) were nitrinergic. Most (96%) received terminations positive for vasoactive intestinal polypeptide (VIP), calcitonin gene related peptide (CGRP) (80%), and galanin (59%). The neuronal somata of 14% also contained VIP, while 10% had galanin. Of the NADPH-diaphorase containing fibers seen in the muscle layers, many had closely associated VIP and galanin, but only rarely CGRP and substance P. Thus, despite abundant representation of both peptidergic and nitrinergic systems in oesophageal smooth muscle, only VIP and galanin colocalised to any significant extent with the nitrinergic elements. These findings provide morphological support for the role of nitric oxide as the non-adrenergic non-cholinergic inhibitory mediator in the human oesophagus and for its possible interactive role with the peptidergic system.

Adult↗

Primary renal carcinoid. Case report and literature review.

We report a case of primary renal carcinoid, which is a very rare neoplasm: to our knowledge, only 19 cases have been previously reported. The tumor displayed histologic features typical of carcinoid tumors from other sites, including growth in nests and ribbons, uniform cells with finely granular, eosinophilic cytoplasm, and stippled chromatin. Electron microscopy confirmed the presence of membrane-bound dense-core granules. Immunohistochemical analysis revealed staining for chromogranin A, neuron-specific enolase, Leu-7, and synaptophysin, as well as pancreatic polypeptide. An interesting finding was the positive staining for prostatic acid phosphatase, while staining for prostate-specific antigen was negative. Although prostatic acid phosphatase is commonly seen in primary gastrointestinal hindgut carcinoids, in this case a primary hindgut carcinoid was ruled out by clinical examination and endoscopy. The patient developed metastases to the liver, but was well and without symptoms 15 months after diagnosis.

Acid Phosphatase↗

The establishment and characterization of a peripheral neuroepithelioma cell line in soft tissue of extremity.

BACKGROUND: The histogenetic and biologic features of peripheral neuroepithelioma (PN) are still a matter of controversy. More detailed analyses might be facilitated by permanent PN cell lines. However, there have been only a few reports on the establishment of a PN cell line. EXPERIMENTAL DESIGN: We established and characterized a PN cell line and further carried out experiments for potentiality of drug-induced neural differentiation. RESULTS: The cultured cells were spindle shaped with slender cytoplasmic processes. The histologic features of transplanted tumors in nude mice were essentially the same as those of the original tumor. Immunohistochemically, the neuroectodermal characteristics of the cell line were demonstrated by positive stain for neuron specific enolase, glial fibrillary acidic protein, S-100 protein, neurofilament, and beta 2-microglobulin. Ultrastructurally, microtubules and dense core granules were observed in the cultured cells. Northern blot analyses revealed that c-myc was overexpressed in the cell line, whereas N-myc was not. The cell line showed neural differentiation after treatment with cAMP elevating reagents and nerve growth factor (NGF). The synergistic effects of cAMP analog and NGF on the neurite outgrowth were also observed. Furthermore, a cAMP-dependent protein kinase (PKA) inhibitor strongly blocked the action of cAMP analog, although it was not able to inhibit the same action of NGF. These findings suggested that the neurite outgrowth induced by the cAMP analog requires activation of PKA, whereas the same actions of NGF do not mediate such a pathway involving PKA activation. CONCLUSIONS: This is, to our knowledge, the first NGF responsive cell line derived from PN. This cell line might be valuable for further investigations of signal transduction pathways induced by cAMP analogs and NGF, for more precise analyses of the biological characteristics of PN, and finally, for the identification of differences between PN and several related tumors.

Adult↗

Degradation and regurgitation of extracellular proteins by cultured mouse peritoneal macrophages and baby hamster kidney fibroblasts. Kinetic evidence that the transfer of proteins to lysosomes is not irreversible.

The uptake and degradation of bovine serum albumin (BSA), bovine liver catalase, and rabbit muscle enolase have been studied in cultured mouse peritoneal macrophages (MPM) and baby hamster kidney fibroblasts (BHK cells). Rates constant for the uptake of the three proteins by MPM were similar. In addition, BSA accumulation was independent of BSA concentration in the uptake medium and was not inhibited by a large excess of serum, suggesting that protein accumulation was by fluid phase pinocytosis. Following an overnight uptake, 20-30% of the accumulated protein was subsequently regurgitated into the medium in a trichloroacetic acid/phosphotungstic acid-precipitable form. This material co-migrated with the authentic protein during molecular sieve chromatography on Sephadex G-50. The rates of appearance of trichloroacetic acid/phosphotungstic acid-insoluble products were greater than expected for cell death and leakage. The observed first order rate constants, kobs, for the appearance of trichloroacetic acid/phosphotungstic acid-soluble and trichloroacetic acid/phosphotungstic acid-insoluble products in the culture medium were identical, indicating that both products were released in parallel from MPM and BHK cells. The kobs for intracellular BSA degradation and regurgitation were independent of the initial BSA concentration in the uptake medium, but were decreased about 35% when degradation was allowed to proceed in the presence of high concentrations of serum. Degradation was also inhibited by chloroquine and pepstatin. Inhibition of degradation was accompanied by an increase in the total amount of regurgitated protein appearing in the medium. Remarkably, however, these inhibitors also decreased kobs for regurgitation, thereby preserving the similarity in the observed rate constants for the appearance of trichloroacetic acid/phosphotungstic acid-soluble and trichloroacetic acid/phosphotungstic acid-insoluble products. These and other results were inconsistent with desorption of proteins from the surface of the culture dish or the surface of cells as the source of the trichloroacetic acid/phosphotungstic acid-insoluble label appearing in the medium.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

Multipotent stem/progenitor cells with similar properties arise from two neurogenic regions of adult human brain.

Recent in vitro studies have shown that the periventricular subependymal zone (SEZ) of the rodent brain is capable of de novo generation of neurons and glia. There is less information available on neurogenesis in the adult human brain, and no study has shown the clonal generation of neurons and glia from in vitro-generated "neurospheres." Here we describe the isolation of proliferative stem/progenitor cells within neurospheres from two different regions, the SEZ and the hippocampus, from surgical biopsy specimens of adult (24-57 years) human brain. Using light and electron microscopy; immunocytochemistry for a variety of neuronal, glial, and developmental (including extracellular matrix; ECM) markers; and the reverse transcriptase polymerase chain reaction to demonstrate different gene transcripts found in neurospheres, it is shown that the adult human brain harbors a complex population of stem/progenitor cells that can generate neuronal and glial progeny under particular in vitro growth conditions. These methods also show that these neurospheres contain both neurons and glia and demonstrate regional similarities at the mRNA level, indicating common stem/progenitor cell types within two different neurogenic regions of the adult human brain. In addition to the synthesis of developmentally regulated molecules such as the ECM protein tenascin-C, a variety of other genes (e.g., Pax 6) and proteins (e.g. , Bcl-2) involved in cell survival and differentiation are expressed by adult human brain neurospheres.

Adolescent↗

Grafts of adult subependymal zone neuronal progenitor cells rescue hemiparkinsonian behavioral decline.

Neuronal progenitor cells (NPCs) residing in the adult subependymal zone (SEZ) are a potential source of expandable cells for autologous transplantation to treat Parkinson's Disease and other types of brain injury. We have previously demonstrated the capacity of transplanted adult SEZ NPCs for heterotypic differentiation in the hippocampus. To further characterize the therapeutic potential of these cells, NPCs expanded from the adult rat SEZ were grafted to the striatum of normal and 6-OHDA lesioned adult rats. Grafted cells were assessed for neuronal differentiation, and lesioned animals were tested for amphetamine-induced rotational asymmetry. In addition, the effect of inducing differentiation in vitro prior to transplantation was assessed. Although grafted cells survived after 2 weeks in all animals, neither striatal deafferentation nor in vitro induction of differentiation resulted in significant neuronal differentiation of transplanted cells. Grafts, however, did produce a behavioral effect. While sham animals exhibited increased rotational behavior (+67%) from 2 to 4 weeks post-lesioning, grafted animals did not (-21%). Grafted cells continued to express nestin at the survival time point, and dopamine transporter (DAT) immunoreactivity was restored in the graft body. These results suggest that although neither the normal nor the deafferented striatum alone support the neuronal differentiation of transplanted adult SEZ NPCs, grafts maintaining a progenitor phenotype may produce a therapeutic benefit.

Animals↗

Mechanisms of the neuroprotective effect of aspirin after oxygen and glucose deprivation in rat forebrain slices.

Acetylsalicylic acid (ASA, Aspirin) is an anti-inflammatory drug with a wide spectrum of pharmacological activities and multiple sites of action. Apart from its preventive actions against stroke due to its antithrombotic properties, recent data in the literature suggest that high concentrations of ASA also exert direct neuroprotective effects. We have used an in vitro model of brain ischaemia using rat forebrain slices deprived of oxygen and glucose to test ASA neuroprotective properties. We have found that ASA inhibits neuronal damage at concentrations lower than those previously reported (0.1-0.5 mM), and that these effects correlate with the inhibition of excitatory amino acid release, of NF-kappaB translocation to the nucleus and iNOS expression caused by ASA. All of these three mechanisms may mediate the neuroprotective effects of this drug. Our results also show that the effects of ASA are independent of COX inhibition. Taken together, our present findings show that ASA is neuroprotective in an in vitro model of brain ischaemia at doses close to those recommended for its antithrombotic effects.

Animals↗

Cloning, expression and mutagenesis of a subunit contact of rabbit muscle-specific (betabeta) enolase.

The cDNA for rabbit muscle-specific (betabeta) enolase was cloned, sequenced and expressed in Escherichia coli. This betabeta-enolase differs at eight positions from that sequenced by Chin (17). Site-directed mutagenesis was used to change residue 414 from glutamate to leucine, thereby abolishing a salt bridge involved in subunit contacts. Recombinant wild-type and mutant enolase were purified from E. coli and compared to enolase isolated from rabbit muscle. Molecular weights were determined by mass spectrometry. All three betabeta-enolases had similar kinetics, and UV and circular dichroism (CD) spectra. The mutant enolase was far more sensitive to inactivation by pressure, by KCl or EDTA, and by sodium perchlorate. We confirmed, by analytical ultracentrifugation, that the sodium perchlorate inactivation was due to dissociation. DeltaG(o) for dissociation of enolase was decreased from 49.7 kJ/mol for the wild-type enzyme to 42.3 kJ/mol for the mutant. In contrast to the wild-type enzyme, perchlorate inactivation of E414L was accompanied by a small loss of secondary structure.

Amino Acid Sequence↗

Dietary effects of copper and iron deficiency on rat intestine: a differential display proteome analysis.

Copper and iron are cofactors of many metallo-proteins that accomplish vital functions, such as oxygen and electron transport. Specific metabolic pathways have been selected through evolution, although still not fully elucidated, to confine the dangerous reactivity of their free ionic forms. Inadequate supply of both metals can severely affect basic physiological functions. A differential analysis of the rat intestinal proteome evidenced the following dietary copper- and iron-deficiencies, i.e., significant changes in the levels of proteins belonging to different functional classes (glucose and fatty acid metabolism, molecular chaperones, cytoskeleton plasticity, vitamin transporters). The presented results bring new perspectives to understand the role of copper and iron in the metabolic pathways and provide novel diagnostic tools to characterize the effects of subclinical deficiencies of both metals in unbalanced nutritional disorders.

Animals↗

Phylogenetic distribution of neuron-specific enolase.

Neurons and neuroendocrine cells contain a unique isoenzyme of the glycolytic enzyme enolase which is not found in other cells. This acidic enolase isoenzyme has been designated neuron specific enolase or NSE and is easily identified by its elution on DEAE sephadex. The present study shows that brain tissue from species such as yeast, fish and frog do not contain appreciable amounts of acidic "NSE-like" enolase suggesting that lower species do not have this neuronal isoenzyme.

Animals↗