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.     

Molecular cloning and the nucleotide sequence of cDNA to mRNA for non-neuronal enolase (alpha alpha enolase) of rat brain and liver.

The nucleotide sequence for alpha alpha enolase (non-neuronal enolase: NNE) of rat brain and liver was determined from recombinant cDNA clones. The sequence was composed of 1722 bp which included the 1299 bp of the complete coding region, the 108 bp of the 5'-noncoding region and the 312 bp of the 3'-noncoding region containing a polyadenylation signal. In addition, the poly(A) tail was also found. A potential ribosome-binding site was located 30 nucleotides upstream to the initiation codon in the 5'-noncoding region. The amino acid sequence deduced from the nucleotide sequence was 433 amino acids in length and showed very high homology (82%) to the amino acid sequence of gamma gamma enolase (neuron-specific enolase: NSE), although the nucleotide sequence showed slightly lower homology (75%). The size of NNE mRNA was approximately 1800 bases by Northern transfer analysis and much shorter than that of NSE mRNA (2400 bases) indicating a short 3'-noncoding region. A dot-blot hybridization and Northern transfer analysis of cytoplasmic RNA from the developing rat brains using a labeled 3'-noncoding region of cDNA (no homology between NSE and NNE) showed a decrease of NNE mRNA at around 10 postnatal days and then a gradual increase to adult age without changes of mRNA size. Liver mRNA did not show any significant change during development.     

Characterization of a maize cDNA that complements an enolase-deficient mutant of Escherichia coli

A cDNA encoding maize enolase (2-phospho-D-glycerate hydrolase) was purified by functional genetic complementation using an enolase deficient mutant of Escherichia coli, DF261. This cDNA, pZM245, was characterized by restriction mapping and DNA sequence analysis. The cDNA contained an open reading frame encoding a protein of 446 amino acids with a high degree of similarity to enolase sequences from other organisms (72% identity to yeast enolase and 82% identity to human enolase). The pZM245 contains a correctly positioned consensus prokaryotic translation initiation sequence. The specific activity of enolase in maize increases to about twice its initial level after 48 hours of anaerobiosis. Northern-blot analysis showed a five-fold anaerobic induction in enolase mRNA, while heat shock or cold shock increased enolase mRNA levels only slightly. Southern-blot analysis of maize genomic DNA indicated that there is one copy of the pZM245 hybridizing sequence per haploid genome in maize.     

Characterization of squid enolase mRNA: Sequence analysis,tissue distribution,and axonal localization

Enolase is a glycolytic enzyme whose amino acid sequence is highly conserved across a wide range of animal species. In mammals, enolase is known to be a dimeric protein composed of distinct but closely related subunits: (non-neuronal), (muscle-specific), and (neuron-specific). However, little information is available on the primary sequence of enolase in invertebrates. Here we report the isolation of two overlapping cDNA clones and the putative primary structure of the enzyme from the squid (Loligo pealii) nervous system. The composite sequence of those cDNA clones is 1575 bp and contains the entire coding region (1302 bp), as well as 66 and 207 bp of 5 and 3 untranslated sequence, respectively. Cross-species comparison of enolase primary structure reveals that squid enolase shares over 70% sequence identity to vertebrate forms of the enzyme. The greatest degree of sequence similarity was manifest to the isoform of the human homologue. Results of Northern analysis revealed a single 1.6 kb mRNA species, the relative abundance of which differs approximately 10-fold between various tissues. Interestingly, evidence derived from in situ hybridization and polymerase chain reaction experiments indicate that the mRNA encoding enolase is present in the squid giant axon.     

Purification, characterization, and distribution of enolase isozymes in chicken

Chicken brain enolase was found to show multiple forms (I, II and III) separable by DEAE-cellulose column chromatography, whereas enolase from chicken skeletal muscle showed a single form. Brain enolase I, enolase III and muscle enolase were purified to electrophoretic homogeneity. These three isozymes were dimeric enzymes, each being composed of two identical subunits, alpha, gamma and beta, having molecular weight of 51,000 +/- 600, 52,000 +/- 550 and 51,500 +/- 650, respectively, as determined by SDS-polyacrylamide gel electrophoresis analysis. Brain enolases I, II and III and muscle enolase had similar catalytic parameters, including almost the same Km values and pH optima. Specific antibodies against brain enolase I, enolase III and muscle enolase, raised in rabbit, showed no cross-reactivity with each other. Antibodies for brain enolases I and III also reacted with brain enolase II, indicating that brain enolase II was the hybrid form (alpha gamma) of brain enolases I (alpha alpha) and III (gamma gamma). Enolases from chicken liver, kidney and heart reacted with the antisera for brain enolase I, but not with those for brain enolase III or muscle enolase. Developmental changes in enolase isozyme distribution were observed in chicken brain and skeletal muscle. In brain, the alpha gamma and gamma gamma forms were not detected in the early embryonic stage and increased gradually during the development of the brain, whereas the alpha alpha form existed at an almost constant level during development. In skeletal muscle, complete switching from alpha alpha enolase to beta beta was observed during the period around hatching.     

Changes in levels of translatable mRNA for neuron-specific enolase and non-neuronal enolase during development of rat brain and liver

Neuron-specific enolase (NSE), and non-neuronal enolase (NNE) which exists in many tissues including liver but is localized in glial cells within the nervous system, were synthesized in the rabbit reticulocyte cell-free translation system programmed with brain mRNAs. The in vitro synthesized NSE and NNE were indistinguishable from the two enzymes purified from rat brains. NSE mRNA activity was found only in brain RNAs, while NNE mRNA activity existed in brain RNAs as well as liver RNAs. In developing brains, the level of translatable NSE mRNA was low at the embryonic stage and at birth, increased rapidly from about 10 days postnatal, and reached the adult level, while that of NNE mRNA was high at the embryonic stage and at birth, followed by a slight decrease then a gradual rise to adult levels. These changes correlated with the developmentally regulated appearance and accumulation pattern of each of the two enzymes. These results suggest that the levels of NSE and NNE are controlled primarily by the level of each of the two translatable mRNAs. In developing livers, only the NNE mRNA activity was detected and its level generally paralleled the changes in the level of NNE.     

Expression, purification and the 1.8 angstroms resolution crystal structure of human neuron specific enolase

Human neuron-specific enolase (NSE) or isozyme gamma has been expressed with a C-terminal His-tag in Escherichia coli. The enzyme has been purified, crystallized and its crystal structure determined. In the crystals the enzyme forms the asymmetric complex NSE x Mg2 x SO4/NSE x Mg x Cl, where "/" separates the dimer subunits. The subunit that contains the sulfate (or phosphate) ion and two magnesium ions is in the closed conformation observed in enolase complexes with the substrate or its analogues; the other subunit is in the open conformation observed in enolase subunits without bound substrate or analogues. This indicates negative cooperativity for ligand binding between subunits. Electrostatic charge differences between isozymes alpha and gamma, -19 at physiological pH, are concentrated in the regions of the molecular surface that are negatively charged in alpha, i.e. surface areas negatively charged in alpha are more negatively charged in gamma, while areas that are neutral or positively charged tend to be charge-conserved.     

Molecular cloning and nucleotide sequence of cDNA encoding the rat kidney S-adenosylmethionine synthetase.

We previously reported the isolation of a cDNA encoding the liver-specific isozyme of rat S-adenosylmethionine synthetase from a lambda gt11 rat liver cDNA library. Using this cDNA as a probe, we have isolated and sequenced cDNA clones for the rat kidney S-adenosylmethionine synthetase (extrahepatic isoenzyme) from a lambda gt11 rat kidney cDNA library. The complete coding sequence of this enzyme mRNA was obtained from two overlapping cDNA clones. The amino acid sequence deduced from the cDNAs indicates that this enzyme contains 395 amino acids and has a molecular mass of 43,715 Da. The predicted amino acid sequence of this protein shares 85% similarity with that of rat liver S-adenosylmethionine synthetase. This result suggests that kidney and liver isoenzymes may have originated from a common ancestral gene. In addition, comparison of known S-adenosylmethionine synthetase sequences among different species also shows that these proteins have a high degree of similarity. The distribution of kidney- and liver-type S-adenosylmethionine synthetase mRNAs in kidney, liver, brain, and testis were examined by RNA blot hybridization analysis with probes specific for the respective mRNAs. A 3.4-kilobase (kb) mRNA species hybridizable with a probe for kidney S-adenosylmethionine synthetase was found in all tissues examined except for liver, while a 3.4-kb mRNA species hybridizable with a probe for liver S-adenosylmethionine synthetase was only present in the liver. The 3.4-kb kidney-type isozyme mRNA showed the same molecular size as the liver-type isozyme mRNA. Thus, kidney- and liver-type S-adenosylmethionine synthetase isozyme mRNAs were expressed in various tissues with different tissue specificities.     

Complete amino acid sequence of the type II isozyme of rat hexokinase, deduced from the cloned cDNA: comparison with a hexokinase from novikoff ascites tumor

The 917-residue amino acid sequence of the Type II isozyme of rat hexokinase has been deduced from the nucleotide sequence of cloned cDNA. The sequences of 197 nucleotides in the 5' untranslated region and 687 bases of the 3' untranslated region have also been determined. A region of overlap between two discrete cDNA clones was confirmed by isolation and sequencing of a genomic DNA clone that spanned the region. Within this region, the 634-nucleotide coding sequence was divided into three exons, each of 150-250 nucleotides; these results suggest that the gene encoding Type II hexokinase is likely to be quite complex. There is extensive similarity between the sequences of the N- and C-terminal halves of the Type II isozyme, as previously seen with the Type I and III isozymes; this is consistent with the view that these enzymes evolved by a process of gene duplication and fusion. A cDNA encoding the entire C-terminal half of a hexokinase from Novikoff ascites tumor cells was also isolated and found to be identical to a cDNA encoding the corresponding region of the Type II isozyme of skeletal muscle. Northern analysis indicated that a single mRNA, approx 5200 nucleotides in length, encoded both the skeletal muscle and the tumor enzymes. These results do not support previous speculation that the hexokinase isozymes of normal tissue are distinct from those of tumors, and suggest the possibility that post-translational modifications of a single protein species might account for apparent differences between the isozymes of normal and tumor tissues.     

Inhibition of human muscle-specific enolase by methylglyoxal and irreversible formation of advanced glycation end products

Methylglyoxal (MG) was studied as an inhibitor and effective glycating factor of human muscle-specific enolase. The inhibition was carried out by the use of a preincubation procedure in the absence of substrate. Experiments were performed in anionic and cationic buffers and showed that inhibition of enolase by methylglyoxal and formation of enolase-derived glycation products arose more effectively in slight alkaline conditions and in the presence of inorganic phosphate. Incubation of 15 micromolar solutions of the enzyme with 2 mM, 3.1 mM and 4.34 mM MG in 100 mM phosphate buffer pH 7.4 for 3 h caused the loss a 32%, 55% and 82% of initial specific activity, respectively. The effect of MG on catalytic properties of enolase was investigated. The enzyme changed the K(M) value for glycolytic substrate 2-phospho-D-glycerate (2-PGA) from 0.2 mM for native enzyme to 0.66 mM in the presence of MG. The affinity of enolase for gluconeogenic substrate phosphoenolpyruvate altered after preincubation with MG in the same manner, but less intensively. MG has no effect on V(max) and optimal pH values. Incubation of enolase with MG for 0-48 h generated high molecular weight protein derivatives. Advanced glycation end products (AGEs) were resistant to proteolytic degradation by trypsin. Magnesium ions enhanced the enzyme inactivation by MG and facilitated AGEs formation. However, the protection for this inhibition in the presence of 2-PGA as glycolytic substrate was observed and AGEs were less effectively formed under these conditions.     

Tissue distribution, developmental profiles and effect of denervation of enolase isozymes in rat muscles

The tissue distribution of muscle-type alpha beta and beta beta enolases in rats were determined with the sandwich-type enzyme immunoassay method which utilized the purified antibodies specific to the alpha and to the beta subunit of enolase, and beta-D-galactosidase from Escherichia coli as label. All the tissues examined contained detectable levels of both alpha beta and beta beta enolases. The beta beta enolase was found at high levels in the skeletal muscle tissues (tongue, esophagus, diaphragm and leg muscles) and in the cartilages (xipoid process and auricular cartilage). The alpha beta enolase was distributed at a relatively high concentration in the heart and in the above-mentioned tissues. The beta beta enolase in the leg muscles, diaphragm and tongue was present on the day of birth at a concentration higher than that of the alpha alpha and alpha beta enolases, and its concentration further increased in a manner apparently related to the functional state of each tissue. Denervation of the leg muscles by cutting the sciatic nerve in adult rats resulted in a drastic change in the isozymes profile. The concentration of beta beta enolase in the tibialis anterior gastrocnemius lateralis and extensor digitorum longus (about 800 pmol/mg protein) decreased to about a half in a few weeks after denervation. In contrast, the concentrations of alpha alpha (2 pmol/mg) and alpha beta (80 pmol/mg) usually showed a slight increase by the treatment (alpha alpha, 7 pmol/mg; alpha beta, 100 pmol/mg after 2 weeks). As compared with these three muscles, the soleus had normally a low enolase level and the effect of denervation was less drastic. These results seem to suggest that the concentration of beta beta enolase is closely correlated with the functional state of the muscle tissue.