Mechanism of enolase: the crystal structure of asymmetric dimer enolase-2-phospho-D-glycerate/enolase-phosphoenolpyruvate at 2.0 A resolution

Structural snapshots of Mycobacterium tuberculosis enolase reveal dual mode of 2PG binding and its implication in enzyme catalysis

Enolase, a ubiquitous enzyme, catalyzes the reversible conversion of 2-phosphoglycerate (2PG) to phosphoenolpyruvate (PEP) in the glycolytic pathway of organisms of all three domains of life. The underlying mechanism of the 2PG to PEP conversion has been studied in great detail in previous work, however that of the reverse reaction remains to be explored. Here we present structural snapshots of Mycobacterium tuberculosis (Mtb) enolase in apo, PEP-bound and two 2PG-bound forms as it catalyzes the conversion of PEP to 2PG. The two 2PG-bound complex structures differed in the conformation of the bound product (2PG) viz the widely reported canonical conformation and a novel binding pose, which we refer to here as the alternate conformation. Notably, we observed two major differences compared with the forward reaction: the presence of MgB is non-obligatory for the reaction and 2PG assumes an alternate conformation that is likely to facilitate its dissociation from the active site. Molecular dynamics studies and binding free energy calculations further substantiate that the alternate conformation of 2PG causes distortions in both metal ion coordination and hydrogen-bonding interactions, resulting in an increased flexibility of the active-site loops and aiding product release. Taken together, this study presents a probable mechanism involved in PEP to 2PG catalysis that is likely to be mediated by the conformational change of 2PG at the active site.

Enolase Inhibitors as Early Lead Therapeutics against Trypanosoma brucei

Glucose metabolism is critical for the African trypanosome, Trypanosoma brucei, serving as the lone source of ATP production for the bloodstream form (BSF) parasite in the glucose-rich environment of the host blood. Recently, phosphonate inhibitors of human enolase (ENO), the enzyme responsible for the interconversion of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP) in glycolysis or PEP to 2-PG in gluconeogenesis, have been developed for the treatment of glioblastoma multiforme (GBM). Here, we have tested these agents against T. brucei ENO (TbENO) and found the compounds to be potent enzyme inhibitors and trypanocides. For example, (1-hydroxy-2-oxopyrrolidin-3-yl) phosphonic acid (deoxy-SF2312) was a potent enzyme inhibitor (IC50 value of 0.60 ± 0.23 µM), while a six-membered ring-bearing phosphonate, (1-hydroxy-2-oxopiperidin-3-yl) phosphonic acid (HEX), was less potent (IC50 value of 2.1 ± 1.1 µM). An analog with a larger seven-membered ring, (1-hydroxy-2-oxoazepan-3-yl) phosphonic acid (HEPTA), was not active. Molecular docking simulations revealed that deoxy-SF2312 and HEX had binding affinities of -6.8 and -7.5 kcal/mol, respectively, while the larger HEPTA did not bind as well, with a binding of affinity of -4.8 kcal/mol. None of these compounds were toxic to BSF parasites; however, modification of enzyme-active phosphonates through the addition of pivaloyloxymethyl (POM) groups improved activity against T. brucei, with POM-modified (1,5-dihydroxy-2-oxopyrrolidin-3-yl) phosphonic acid (POMSF) and POMHEX having EC50 values of 0.45 ± 0.10 and 0.61 ± 0.08 µM, respectively. These findings suggest that HEX is a promising lead against T. brucei and that further development of prodrug HEX analogs is warranted.

Effects of Silver Nanoparticles on Physiological and Proteomic Responses of Tobacco (Nicotiana tabacum) Seedlings Are Coating-Dependent

The harmful effects of silver nanoparticles (AgNPs) have been confirmed in many organisms, but the mechanism of their toxicity is not yet fully understood. In biological systems, AgNPs tend to aggregate and dissolve, so they are often stabilized by coatings that influence their physico-chemical properties. In this study, the effects of AgNPs with different coatings [polyvinylpyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB)] on oxidative stress appearance and proteome changes in tobacco (Nicotiana tabacum) seedlings have been examined. To discriminate between the nanoparticulate Ag form from the ionic one, the treatments with AgNO₃, a source of Ag⁺ ions, were also included. Ag uptake and accumulation were found to be similarly effective upon exposure to all treatment types, although positively charged AgNP-CTAB showed less stability and a generally stronger impact on the investigated parameters in comparison with more stable and negatively charged AgNP-PVP and ionic silver (AgNO₃). Both AgNP treatments induced reactive oxygen species (ROS) formation and increased the expression of proteins involved in antioxidant defense, confirming oxidative stress as an important mechanism of AgNP phytotoxicity. However, the mechanism of seedling responses differed depending on the type of AgNP used. The highest AgNP-CTAB concentration and CTAB coating resulted in increased H₂O₂ content and significant damage to lipids, proteins and DNA molecules, as well as a strong activation of antioxidant enzymes, especially CAT and APX. On the other hand, AgNP-PVP and AgNO₃ treatments induced the nonenzymatic antioxidants by significantly increasing the proline and GSH content. Exposure to AgNP-CTAB also resulted in more noticeable changes in the expression of proteins belonging to the defense and stress response, carbohydrate and energy metabolism and storage protein categories in comparison to AgNP-PVP and AgNO₃. Cysteine addition significantly reduced the effects of AgNP-PVP and AgNO₃ for the majority of investigated parameters, indicating that AgNP-PVP toxicity mostly derives from released Ag⁺ ions. AgNP-CTAB effects, however, were not alleviated by cysteine addition, suggesting that their toxicity derives from the intrinsic properties of the nanoparticles and the coating itself.

Immunogenic Proteins of Group B Streptococcus-Potential Antigens in Immunodiagnostic Assay for GBS Detection

Streptococcus agalactiae (Group B Streptococcus, GBS) is an opportunistic pathogen, which asymptomatically colonizes the gastrointestinal and genitourinary tract of up to one third of healthy adults. Nevertheless, GBS carriage in pregnant women may lead to several health issues in newborns causing life threatening infection, such as sepsis, pneumonia or meningitis. Recommended GBS screening in pregnant women significantly reduced morbidity and mortality in infants. Nevertheless, intrapartum antibiotic prophylaxis, recommended following the detection of carriage or in case of lack of a carriage test result for pregnant women who demonstrate certain risk factors, led to the expansion of the adverse phenomenon of bacterial resistance to antibiotics. In our paper, we reviewed some immunogenic GBS proteins, i.e., Alp family proteins, β protein, Lmb, Sip, BibA, FsbA, ScpB, enolase, elongation factor Tu, IMPDH, and GroEL, which possess features characteristic of good candidates for immunodiagnostic assays for GBS carriage detection, such as immunoreactivity and specificity. We assume that they can be used as an alternative diagnostic method to the presently recommended bacteriological cultivation and MALDI.

The Unexplored Importance of Fleeting Chiral Intermediates in Enzyme-Catalyzed Reactions

Decades of extensive research efforts by biochemists, organic chemists, and protein engineers have led to an understanding of the basic mechanisms of essentially all known types of enzymes, but in a formidable number of cases an essential aspect has been overlooked. The occurrence of short-lived chiral intermediates formed by symmetry-breaking of prochiral precursors in enzyme catalyzed reactions has been systematically neglected. We designate these elusive species as fleeting chiral intermediates and analyze such crucial questions as "Do such intermediates occur in homochiral form?" If so, what is the absolute configuration, and why did Nature choose that particular stereoisomeric form, even when the isolable final product may be achiral? Does the absolute configuration of a chiral product depend in any way on the absolute configuration of the fleeting chiral precursor? How does this affect the catalytic proficiency of the enzyme? If these issues continue to be unexplored, then an understanding of the mechanisms of many enzyme types remains incomplete. We have systematized the occurrence of these chiral intermediates according to their structures and enzyme types. This is followed by critical analyses of selected case studies and by final conclusions and perspectives. We hope that the fascinating concept of fleeting chiral intermediates will attract the attention of scientists, thereby opening an exciting new research field.

In vitro inhibition studies of coumarin derivatives on Bos taurus enolase and elucidating their interaction by molecular docking, molecular dynamics simulations and MMGB(PB)SA binding energy calculation

Tropical theileriosis is among the most common vector-borne diseases and caused by Theileria parasites. Theileria annulata is an obligate intracellular protozoan parasite and transmitted to especially Bos taurus and Bos indicus by Hyalomma tick vectors. C8 ([4-(3,4-dimethoxyphenyl)-6,7-dihydroxy-2H-chromen-2-one); C9 (4-(3,4-dihydroxyphenyl)-7,8 dihydroxy-2H-chromen-2-one); C21 (4-(3,4-dihydroxyphenyl)-6,7-dihydroxy-2H-chromen-2 one) were identified as potent Theileria annulata enolase (TaEno) inhibitors in our previous studies. An ideal drug compound must inhibit the target parasite enzyme without inhibiting its homolog in the host. In this study, the inhibitory effect of the compounds previously evaluated on TaEno were tested on the host Bos taurus enolase (BtEno3) by in vitro studies. The interactions of enzyme-coumarin and enzyme-coumarin-substrate by in silico studies were also performed. All of the coumarin derivatives tested showed very low inhibitory effects on B. taurus enolase; 36,87% inhibition at 100 μM concentration for C8, 8,13% inhibition at 100 μM concentration for C9 and 77,69 μM of IC₅₀ value for C21. In addition, these three coumarin derivatives and substrate 2PG were docked into the BtEno3 using molecular docking methods. Molecular interactions between enolase-coumarin and enolase-coumarin-substrate complexes were analyzed using molecular dynamics simulation methods for 100 ns. Estimated free energy of bindings of the substrate 2PG and coumarin derivatives to the BtEno3 were calculated by MM-GB(PB)SA methods. In comparison to the inhibition studies performed on TaEno, C8 and C9 coumarin derivatives remain the possible inhibitor candidates as they inhibit the host enolase at very high concentrations. These two promising compounds will be further analyzed by in vitro and in vivo studies towards developing an alternative drug against tropical theileriosis.

Structural Insights into the Interactions of Candidal Enolase with Human Vitronectin, Fibronectin and Plasminogen

Significant amounts of enolase—a cytosolic enzyme involved in the glycolysis pathway—are exposed on the cell surface of Candida yeast. It has been hypothesized that this exposed enolase form contributes to infection-related phenomena such as fungal adhesion to human tissues, and the activation of fibrinolysis and extracellular matrix degradation. The aim of the present study was to characterize, in structural terms, the protein-protein interactions underlying these moonlighting functions of enolase. The tight binding of human vitronectin, fibronectin and plasminogen by purified C. albicans and C. tropicalis enolases was quantitatively analyzed by surface plasmon resonance measurements, and the dissociation constants of the formed complexes were determined to be in the 10⁻⁷–10⁻⁸ M range. In contrast, the binding of human proteins by the S.cerevisiae enzyme was much weaker. The chemical cross-linking method was used to map the sites on enolase molecules that come into direct contact with human proteins. An internal motif ₂₃₅DKAGYKGKVGIAMDVASSEFYKDGK₂₅₉ in C. albicans enolase was suggested to contribute to the binding of all three human proteins tested. Models for these interactions were developed and revealed the sites on the enolase molecule that bind human proteins, extensively overlap for these ligands, and are well-separated from the catalytic activity center.

The mechanism of improved gellan gum production by two-stage culture of Sphingomonas paucimobilis

A two-stage culture (with controlled sucrose concentrations and temperatures) of Sphingomonas paucimobilis for gellan gum production has been previously investigated. Herein, the mechanism of a two-stage culture favoring gellan gum overproduction was revealed by analysing the cell-membrane permeability and the proteomics for gellan gum biosynthesis. The two-stage culture, resulted in 79.8% increased content of unsaturated fatty acids, and 3.95% increased ratio of unsaturated to saturated fatty acids in the cell membrane. Moreover, cell membrane permeability increased and thus further enhanced gellan gum biosynthesis. Proteomic analysis results indicated that 13 identified protein spots were involved in energy generation, glycogen biosynthesis, and glycolysis. These findings revealed that two-stage culture impellel carbon flux flow toward gellan gum biosynthesis.

Immunization with recombinant enolase of Sporothrix spp. (rSsEno) confers effective protection against sporotrichosis in mice

In recent years, research has focused on the immunoreactive components of the Sporothrix schenckii cell wall that can be relevant targets for preventive and therapeutic vaccines against sporotrichosis, an emergent worldwide mycosis. In a previous study, we identified a 47-kDa enolase as an immunodominant antigen in mice vaccinated with an adjuvanted mixture of S. schenckii cell wall proteins. Here, we sought to assess the protective potential of a Sporothrix spp. recombinant enolase (rSsEno) formulated with or without the adjuvant Montanide Pet-GelA (PGA) against the S. brasiliensis infection in mice. Mice that were immunized with rSsEno plus PGA showed increased antibody titters against rSsEno and increased median survival time when challenged with S. brasiliensis as compared with mice that had not been immunized or that were immunized with rSsEno alone. Immunization with rSsEno plus PGA induced a predominantly T-helper 1 cytokine pattern after in vitro stimulation of splenic cells with rSsEno: elevated levels of IFN-γ and IL-2, as well as of other cytokines involved in host defense against sporotrichosis, such as TNF-alpha, IL-6, and IL-4. Furthermore, we show for the first time the presence of enolase in the cell wall of both S. schenckii and S. brasiliensis. As a whole, our results suggest that enolase could be used as a potential antigenic target for vaccinal purposes against sporotrichosis.

Substrate-to-Product Conversion Facilitates Active Site Loop Opening in Yeast Enolase: A Molecular Dynamics Study

Yeast enolase serves as a prototype for metalloenzymes with labile, catalytic active site metal ions and is important for glycolysis and fermentation processes. Herein, microsecond molecular dynamics simulations of the protein-substrate and protein-product complexes are conducted to elucidate the mechanism of the opening of catalytically important active site loops. These simulations indicate that conversion of substrate to product is accompanied by diminished metal coordination and hydrogen-bonding interactions, as well as enhanced loop flexibility. Moreover, free energy simulations show that the loop opening is endergonic when substrate is bound but exergonic when product is bound. Thus, the conversion to product weakens the association of the loop with the ligand and binding site, thereby facilitating the loop opening after catalysis and enabling product release. These insights about active site loop motions in enzyme catalysis may be useful in guiding enzyme design efforts.

Survival Factor Gene FgSvf1 Is Required for Normal Growth and Stress Resistance in Fusarium graminearum

Survival factor 1 (Svf1) is a protein involved in cell survival pathways. In Saccharomyces cerevisiae, Svf1 is required for the diauxic growth shift and survival under stress conditions. In this study, we characterized the role of FgSvf1, the Svf1 homolog in the homothallic ascomycete fungus Fusarium graminearum. In the FgSvf1 deletion mutant, conidial germination was delayed, vegetative growth was reduced, and pathogenicity was completely abolished. Although the FgSvf1 deletion mutant produced perithecia, the normal maturation of ascospore was dismissed in deletion mutant. The FgSvf1 deletion mutant also showed reduced resistance to osmotic, fungicide, and cold stress and reduced sensitivity to oxidative stress when compared to the wild-type strain. In addition, we showed that FgSvf1 affects glycolysis, which results in the abnormal vegetative growth in the FgSvf1 deletion mutant. Further, intracellular reactive oxygen species (ROS) accumulated in the FgSvf1 deletion mutant, and this accumulated ROS might be related to the reduced sensitivity to oxidative stress and the reduced resistance to cold stress and fungicide stress. Overall, understanding the role of FgSvf1 in F. graminearum provides a new target to control F. graminearum infections in fields.

Detection and identification of allergens from Canadian mustard varieties of Sinapis alba and Brassica juncea

Currently, information on the allergens profiles of different mustard varieties is rather scarce. Therefore, the objective of this study was to assess protein profiles and immunoglobulin E (IgE)-binding patterns of selected Canadian mustard varieties. Optimization of a non-denaturing protein extraction from the seeds of selected mustard varieties was first undertaken, and the various extracts were quantitatively and qualitatively analyzed by means of protein recovery determination and protein profiling. The IgE-binding patterns of selected mustard seeds extracts were assessed by immunoblotting using sera from mustard sensitized and allergic individuals. In addition to the known mustard allergens—Sin a 2 (11S globulins), Sin a 1, and Bra j 1 (2S albumins)—the presence of other new IgE-binding protein bands was revealed from both Sinapis alba and Brassica juncea varieties. Mass spectrometry (MS) analysis of the in-gel digested IgE-reactive bands identified the unknown ones as being oleosin, β-glucosidase, enolase, and glutathione-S transferase proteins. A bioinformatic comparison of the amino acid sequence of the new IgE-binding mustard proteins with those of know allergens revealed a number of strong homologies that are highly relevant for potential allergic cross-reactivity. Moreover, it was found that Sin a 1, Bra j 1, and cruciferin polypeptides exhibited a stronger IgE reactivity under non-reducing conditions in comparison to reducing conditions, demonstrating the recognition of conformational epitopes. These results further support the utilization of non-denaturing extraction and analysis conditions, as denaturing conditions may lead to failure in the detection of important immunoreactive epitopes.

Identification of Candidate Genes for the Plateau Adaptation of a Tibetan Amphipod, Gammarus lacustris, Through Integration of Genome and Transcriptome Sequencing

The amphipod Gammarus lacustris has been distributing in the Tibetan region with well-known uplifts of the Tibetan plateau. It is hence considered as a good model for investigating stress adaptations of the plateau. Here, we sequenced the whole-genome and full-length transcriptome of G. lacustris, and compared the transcriptome results with its counterpart Gammarus pisinnus from a nearby plain. Our main goal was to provide a genomic resource for investigation of genetic mechanisms, by which G. lacustris adapted to living on the plateau. The final draft genome assembly of G. lacustris was 5.07 gigabases (Gb), and it contained 443,304 scaffolds (>2 kb) with an N50 of 2,578 bp. A total of 8,858 unigenes were predicted in the full-length transcriptome of G. lacustris, with an average gene length of 1,811 bp. Compared with the G. pisinnus transcriptome, 2,672 differentially expressed genes (DEGs) were up-regulated and 2,881 DEGs were down-regulated in the G. lacustris transcriptome. Along with these critical DEGs, several enriched metabolic pathways, such as oxidative phosphorylation, ribosome, cell energy homeostasis, glycolysis and gluconeogenesis, were predicted to play essential roles in the plateau adaptation. In summary, the present study provides a genomic basis for understanding the plateau adaption of G. lacustris, which lays a fundamental basis for further biological and ecological studies on other resident aquatic species in the Tibetan plateau.

Molecular and biochemical characterization of the sunflower (Helianthus annuus L.) cytosolic and plastidial enolases in relation to seed development

In the present study, we describe the molecular and biochemical characterization of sunflower (Helianthus annuus L.) enolase (ENO, EC 4.2.1.11) proteins, which catalyze the formation of phosphoenolpyruvate, the penultimate intermediate in the glycolytic pathway. We cloned and characterized three cDNAs encoding different ENO isoforms from developing sunflower seeds. Studies using fluorescently tagged ENOs confirmed the predicted subcellular localization of ENO isoforms: HaENO1 in the plastid while HaENO2 and HaENO3 were found in the cytosol. The cDNAs were used to express the corresponding 6(His)-tagged proteins in Escherichia coli. The proteins were purified to electrophoretic homogeneity, using immobilized metal ion affinity chromatography, and biochemically characterized. Recombinant HaENO1 and HaENO2, but not HaENO3 were shown to have enolase activity, in agreement with data obtained with the Arabidopsis homolog proteins. Site directed mutagenesis of several critical amino acids was used to attempt to recover enolase activity in recombinant HaENO3, resulting in very small increases that were not additive. A kinetic characterization of the two active isoforms showed that pH had similar effect on their velocity, that they had similar affinity for 2-phosphoglycerate, but that the k_cat/K_m of the plastidial enzyme was higher than that of the cytosolic isoform. Even though HaENO2 was always the most highly expressed transcript, the levels of expression of the three ENO genes were remarkably distinct in all the vegetative and reproductive tissues studied. This indicates that in seeds the conversion of 2-phosphoglycerate to phosphoenolpyruvate takes place through the cytosolic and the plastidial pathways therefore both routes could contribute to the supply of carbon for lipid synthesis. The identity of the main source of carbon during the period of stored products synthesis is discussed.

Acclimation process of cultivating Chlorella vulgaris in toxic excess sludge extract and its response mechanism

Chlorella vulgaris was cultivated in the gradually increased proportion of toxic sludge extracts for acclimation, which was obtained from SBR treated synthetic wastewater containing mixed chlorophenols (2,4,6-trichlorophenol and 4-chlorophenol). The growth of C. vulgaris was obviously improved after acclimation with the cell number in the 100% sludge group was 22.75±0.85∗10⁶cellmL^-1, which was relatively more than the BG11 control group's (20.80±0.35∗10⁶cellmL^-1) and apparently over the 100% sludge group (10.78±0.45∗10⁶cellmL^-1). Compared with the sludge control sludge group, C. vulgaris in the acclimation group gained 24.1% and 18.2% more relative removal rate about TOC and ecotoxicity, respectively. Proteomics analysis showed that protein spots were more clear and centralized and the clarifications of the different protein spots narrowed from 8 to 5 after acclimation. Proteins related to oxidoreducase activity and energy metabolism were over expressed and C. vulgaris could select the metabolic pathways, especially enhanced pyruvate fermentation, TCA cycle, and glycolysis after acclimation, by over accumulating the corresponding vital enzymes. Conclusively, acclimation was a good method to improve the removal ability and growth of C. vulgaris and algae could acclimatize itself to grow upon the toxic sludge extracts by metabolic selection. We suppose acclimation process was a potential method for algae wastewater treatment and algae cultivation without or reduce dilution.

Functions of tryptophan residues in EWGWS insert of Plasmodium falciparum enolase

Plasmodium falciparum enolase (Pfeno) is a dimeric enzyme with multiple moonlighting functions. This enzyme is thus a potential target for anti-malarial treatments. A unique feature of Pfeno is the presence of a pentapeptide insert ¹⁰⁴ EWGWS ¹⁰⁸. The functional role of tryptophan residues in this insert was investigated using site-directed mutagenesis. Replacement of these two Trp residues with alanines (or lysines) resulted in a near complete loss of enolase activity and dissociation of the normal dimeric form into monomers. Molecular modeling indicated that ³⁴⁰R forms π-cation bonds with the aromatic rings of ¹⁰⁵W and ⁴⁶Y. Mutation induced changes in the interactions among these three residues were presumably relayed to the inter-subunit interface via a coil formed by ⁴⁶Y : ⁵⁹Y, resulting in the disruption of a salt bridge between ¹¹R : ⁴²⁵E and a π-cation interaction between ¹¹R : ⁵⁹Y. This led to a drop of ~ 4 kcal·mole^-1 in the inter-subunit docking energy in the mutant, causing a ~ 10³ fold decrease in affinity. Partial restoration of the inter-subunit interactions led to reformation of dimers and also restored a significant fraction of the lost enzyme activity. These results suggested that the perturbations in the conformation of the surface loop containing the insert sequence were relayed to the interface region, causing dimer dissociation that, in turn, disrupted the enzyme's active site. Since Plasmodium enolase is a moonlighting protein with multiple parasite-specific functions, it is likely that these functions may map on to the highly conserved unique insert region of this protein.

ENZYMES

Enolase(EC4.2.1.11).

Complete Molecular and Immunoprotective Characterization of Babesia microti Enolase

The apicomplexan Babesia microti is the primary causative agent of human babesiosis, one of the most broadly distributed tick-borne diseases worldwide. B. microti undergoes a complex lifecycle within both the mammalian host and the tick vector, and employs several different specific molecular mechanisms to enter host cells. Enolase, the key glycolytic enzyme in intracellular glucose metabolism, can also be expressed on the parasite’s outer surface, binds to human plasminogen, and coordinates apicomplexan parasite invasion of host cells, however, it lacks sorting sequences or lipoprotein anchor sites. In the present study, we isolated the coding gene of B. microti enolase (BmEno), expressed it within E. coli and purified the recombinant BmEno protein (rBmEno). Consequently, we confirmed cytoplasmic and surface localization of BmEno via immunofluorescence, and demonstrated that rBmEno catalyzes the dehydration of 2-phospho-D-glycerate to phosphoenolpyruvate. Moreover, our results showed that rBmEno binds to human plasminogen, and that the lysine analog ε-aminocaproic acid significantly inhibited this binding. Furthermore plasminogen bound to rBmEno converts to active plasmin. Additionally, actively immunizing mice with rBmEno could evoke a partial protective immunity against B. microti infection following challenge. In conclusion, B. microti enolase is a multifunctional cytoplasmic protein which is also expressed at the parasitic outer surface, facilitates binding to host plasminogen, and could partially protect hosts against parasite infection.

SF2312 is a natural phosphonate inhibitor of enolase

Despite being critical for energy generation in most forms of life, few if any microbial antibiotics specifically inhibit glycolysis. To develop a specific inhibitor of the glycolytic enzyme Enolase 2 for the treatment of cancers with deletion of Enolase 1, we modeled the synthetic tool compound inhibitor, Phosphonoacetohydroxamate (PhAH) into the active site of human ENO2. A ring-stabilized analogue of PhAH, with the hydroxamic nitrogen linked to the alpha-carbon by an ethylene bridge, was predicted to increase binding affinity by stabilizing the inhibitor in a bound conformation. Unexpectedly, a structure based search revealed that our hypothesized back-bone-stabilized PhAH bears strong similarity to SF2312, a phosphonate antibiotic of unknown mode of action produced by the actinomycete Micromonospora, which is active under anaerobic conditions. Here, we present multiple lines of evidence, including a novel X-ray structure, that SF2312 is a highly potent, low nM inhibitor of Enolase.

Octameric structure of Staphylococcus aureus enolase in complex with phosphoenolpyruvate

Staphylococcus aureus is a Gram-positive bacterium with strong pathogenicity that causes a wide range of infections and diseases. Enolase is an evolutionarily conserved enzyme that plays a key role in energy production through glycolysis. Additionally, enolase is located on the surface of S. aureus and is involved in processes leading to infection. Here, crystal structures of Sa_enolase with and without bound phosphoenolpyruvate (PEP) are presented at 1.6 and 2.45 Å resolution, respectively. The structure reveals an octameric arrangement; however, both dimeric and octameric conformations were observed in solution. Furthermore, enzyme-activity assays show that only the octameric variant is catalytically active. Biochemical and structural studies indicate that the octameric form of Sa_enolase is enzymatically active in vitro and likely also in vivo, while the dimeric form is catalytically inactive and may be involved in other biological processes.

Biochemical and Structural Characterization of Enolase from Chloroflexus aurantiacus: Evidence for a Thermophilic Origin

Enolase catalyzes the conversion of 2-phosphoglycerate to phosphoenolpyruvate during both glycolysis and gluconeogenesis, and is required by all three domains of life. Here, we report the purification and biochemical and structural characterization of enolase from Chloroflexus aurantiacus, a thermophilic anoxygenic phototroph affiliated with the green non-sulfur bacteria. The protein was purified as a homodimer with a subunit molecular weight of 46 kDa. The temperature optimum for enolase catalysis was 80°C, close to the measured thermal stability of the protein which was determined to be 75°C, while the pH optimum for enzyme activity was 6.5. The specific activities of purified enolase determined at 25 and 80°C were 147 and 300 U mg(-1) of protein, respectively. K m values for the 2-phosphoglycerate/phosphoenolpyruvate reaction determined at 25 and 80°C were 0.16 and 0.03 mM, respectively. The K m values for Mg(2+) binding at these temperatures were 2.5 and 1.9 mM, respectively. When compared to enolase from mesophiles, the biochemical and structural properties of enolase from C. aurantiacus are consistent with this being thermally adapted. These data are consistent with the results of our phylogenetic analysis of enolase, which reveal that enolase has a thermophilic origin.

Replacement of Ser108 in Plasmodium falciparum enolase results in weak Mg(II) binding: role of a parasite-specific pentapeptide insert in stabilizing the active conformation of the enzyme

A distinct structural feature of Plasmodium falciparum enolase (Pfeno) is the presence of a five amino acid insert -104EWGWS108- that is not found in host enolases. Its conservation among apicomplexan enolases has raised the possibility of its involvement in some important physiological function(s). Deletion of this sequence is known to lower k(cat)/K(m), increase K(a) for Mg(II) and convert dimer into monomers (Vora HK, Shaik FR, Pal-Bhowmick I, Mout R & Jarori GK (2009) Arch Biochem Biophys 485, 128-138). These authors also raised the possibility of the formation of an H-bond between Ser108 and Leu49 that could stabilize the apo-Pfeno in an active closed conformation that has high affinity for Mg(II). Here, we examined the effect of replacement of Ser108 with Gly/Ala/Thr on enzyme activity, Mg(II) binding affinity, conformational states and oligomeric structure and compared it with native recombinant Pfeno. The results obtained support the view that Ser108 is likely to be involved in the formation of certain crucial H-bonds with Leu49. The presence of these interactions can stabilize apo-Pfeno in an active closed conformation similar to that of Mg(II) bound yeast enolase. As predicted, S108G/A-Pfeno variants (where Ser108-Leu49 H-bonds are likely to be disrupted) were found to exist in an open conformation and had low affinity for Mg(II). They also required Mg(II) induced conformational changes to acquire the active closed conformational state essential for catalysis. The possible physiological relevance of apo-Pfeno being in such an active state is discussed.

The structure of bradyzoite-specific enolase from Toxoplasma gondii reveals insights into its dual cytoplasmic and nuclear functions

In addition to catalyzing a central step in glycolysis, enolase assumes a remarkably diverse set of secondary functions in different organisms, including transcription regulation as documented for the oncogene c-Myc promoter-binding protein 1. The apicomplexan parasite Toxoplasma gondii differentially expresses two nuclear-localized, plant-like enolases: enolase 1 (TgENO1) in the latent bradyzoite cyst stage and enolase 2 (TgENO2) in the rapidly replicative tachyzoite stage. A 2.75 Å resolution crystal structure of bradyzoite enolase 1, the second structure to be reported of a bradyzoite-specific protein in Toxoplasma, captures an open conformational state and reveals that distinctive plant-like insertions are located on surface loops. The enolase 1 structure reveals that a unique residue, Glu164, in catalytic loop 2 may account for the lower activity of this cyst-stage isozyme. Recombinant TgENO1 specifically binds to a TTTTCT DNA motif present in the cyst matrix antigen 1 (TgMAG1) gene promoter as demonstrated by gel retardation. Furthermore, direct physical interactions of both nuclear TgENO1 and TgENO2 with the TgMAG1 gene promoter are demonstrated in vivo using chromatin immunoprecipitation (ChIP) assays. Structural and biochemical studies reveal that T. gondii enolase functions are multifaceted, including the coordination of gene regulation in parasitic stage development. Enolase 1 provides a potential lead in the design of drugs against Toxoplasma brain cysts.

A novel feature extraction scheme for prediction of protein-protein interaction sites

Identifying protein-protein interaction (PPI) sites plays an important and challenging role in some topics of biology. Although many methods have been proposed, this problem is still far away to be solved. Here, a feature selection approach with an 11-sliding window and random forest algorithm is proposed, which is called DX-RF. This method has achieved an accuracy of 88.79%, recall of 82.09%, and precision of 85.76% with top-ranked 34 features on the Hetero test dataset and has 91.6% accuracy, 89.2% precision, 83.54% recall with top-ranked 25 features set on the Homo test dataset. Compared to other methods, the results indicate that the DX-RF method has a strong ability to select relevance features to get a higher performance. Moreover, in order to further understand protein interactions, feature analysis in this study is also performed.

CIP2A regulates cancer metabolism and CREB phosphorylation in non-small cell lung cancer

The cancerous inhibitor of protein phosphatase 2A (CIP2A) is a recently characterized endogenous inhibitor of the phosphatase activity of protein phosphatase 2A (PP2A), which extends the half-life of oncogenic protein c-myc and promotes in vivo tumor growth. The function of CIP2A in cancer progression is still poorly understood. To uncover the underlying mechanism of CIP2A-mediated cell proliferation, we implemented a two-dimensional electrophoresis (2DE)-based proteomic approach to examine lung cancer cell H1299 with and without CIP2A. We found 47 proteins differentially expressed where 19 proteins were upregulated and 28 proteins were downregulated. These were categorized into functional groups such as metabolism (25%), transcriptional and translational control (23%), and the signaling pathway and protein degradation (20%). On one hand, we validate our proteomic work by measuring the metabolic change. The knockdown of CIP2A decreased the expression of LDH-A as well as the enzymatic activity, accompanying with a decreased lactate production, an increased NADH/NAD+ ratio and ROS production. On the other hand, we found that CIP2A may regulate CREB activity through bioinformatics analysis. Our following experiments showed that, CIP2A positively regulated the phosphorylation of CREB in response to the serum treatment. Therefore, our proteomic study suggested that CIP2A mediates cancer progression through the metabolic pathway and intracellular signaling cascade.

Proteomic analysis of zoxamide-induced changes in Phytophthora cactorum

In this study, the global proteomic response of Phytophthora cactorum to zoxamide was evaluated using a two-dimensional gel electrophoresis (2-DE)-based proteomic approach. Among the 21 proteins identified by matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF/TOF MS), four cytoskeleton-related proteins were down-regulated upon addition of zoxamide. Five detoxification metabolism enzymes, seven sugar metabolism proteins and one mitochondria-related protein were up-regulated by more than 2-fold in response to zoxamide. Taken together, these results suggest that zoxamide can decrease the expression of cytoskeleton-related proteins of P. cactorum, resulting in cell death; however, the up-regulation of detoxification metabolism-related enzymes may protect P. cactorum against zoxamide, and the up-regulation of proteins related to sugar metabolism and mitochondria may lead to the generation of more energy for detoxification metabolism. These data also suggest that proteomics may be useful not only in exploring the mode of action of fungicides but also for gaining insight into the resistance mechanisms that pathogens employ against fungicides.

α-Enolase, a multifunctional protein: its role on pathophysiological situations

α-Enolase is a key glycolytic enzyme in the cytoplasm of prokaryotic and eukaryotic cells and is considered a multifunctional protein. α-enolase is expressed on the surface of several cell types, where it acts as a plasminogen receptor, concentrating proteolytic plasmin activity on the cell surface. In addition to glycolytic enzyme and plasminogen receptor functions, α-Enolase appears to have other cellular functions and subcellular localizations that are distinct from its well-established function in glycolysis. Furthermore, differential expression of α-enolase has been related to several pathologies, such as cancer, Alzheimer's disease, and rheumatoid arthritis, among others. We have identified α-enolase as a plasminogen receptor in several cell types. In particular, we have analyzed its role in myogenesis, as an example of extracellular remodelling process. We have shown that α-enolase is expressed on the cell surface of differentiating myocytes, and that inhibitors of α-enolase/plasminogen binding block myogenic fusion in vitro and skeletal muscle regeneration in mice. α-Enolase could be considered as a marker of pathological stress in a high number of diseases, performing several of its multiple functions, mainly as plasminogen receptor. This paper is focused on the multiple roles of the α-enolase/plasminogen axis, related to several pathologies.

Anticancer agents that counteract tumor glycolysis

Can we consider cancer to be a "metabolic disease"? Tumors are the result of a metabolic selection, forming tissues composed of heterogeneous cells that generally express an overactive metabolism as a common feature. In fact, cancer cells have increased needs for both energy and biosynthetic intermediates to support their growth and invasiveness. However, their high proliferation rate often generates regions that are insufficiently oxygenated. Therefore, their carbohydrate metabolism must rely mostly on a glycolytic process that is uncoupled from oxidative phosphorylation. This metabolic switch, also known as the Warburg effect, constitutes a fundamental adaptation of tumor cells to a relatively hostile environment, and supports the evolution of aggressive and metastatic phenotypes. As a result, tumor glycolysis may constitute an attractive target for cancer therapy. This approach has often raised concerns that antiglycolytic agents may cause serious side effects toward normal cells. The key to selective action against cancer cells can be found in their hyperbolic addiction to glycolysis, which may be exploited to generate new anticancer drugs with minimal toxicity. There is growing evidence to support many glycolytic enzymes and transporters as suitable candidate targets for cancer therapy. Herein we review some of the most relevant antiglycolytic agents that have been investigated thus far for the treatment of cancer.

Structures of asymmetric complexes of human neuron specific enolase with resolved substrate and product and an analogous complex with two inhibitors indicate subunit interaction and inhibitor cooperativity

In the presence of magnesium, enolase catalyzes the dehydration of 2-phospho-d-glycerate (PGA) to phosphoenolpyruvate (PEP) in glycolysis and the reverse reaction in gluconeogensis at comparable rates. The structure of human neuron specific enolase (hNSE) crystals soaked in PGA showed that the enzyme is active in the crystals and produced PEP; conversely soaking in PEP produced PGA. Moreover, the hNSE dimer contains PGA bound in one subunit and PEP or a mixture of PEP and PGA in the other. Crystals soaked in a mixture of competitive inhibitors tartronate semialdehyde phosphate (TSP) and lactic acid phosphate (LAP) showed asymmetry with TSP binding in the same site as PGA and LAP in the PEP site. Kinetic studies showed that the inhibition of NSE by mixtures of TSP and LAP is stronger than predicted for independently acting inhibitors. This indicates that in some cases inhibition of homodimeric enzymes by mixtures of inhibitors ("heteroinhibition") may offer advantages over single inhibitors.

Changes of protein profile in fresh-cut lotus tuber before and after browning

Browning is a critical problem, which often limits the shelf life and marketability in fresh-cut lotus tuber. Proteome level changes in response to the browning metabolism were investigated using two-dimensional electrophoresis (2-DE) and MALDI-TOF-TOF. A total of 34 functional protein spots were identified by comparing 2-DE protein patterns of fresh-cut lotus tuber before and after browning. These 34 identified proteins could be classified into 7 functional groups based on the NCBI database, that is, material and energy metabolism (35%), stress response (20%), respiration metabolism (12%), cell structure (12%), signal transduction (6%), gene expression regulation (6%), and unclassified proteins (9%). The group with the greatest difference in protein expression was related to material metabolism and regulation, reactive oxygen species metabolism, and respiratory control. The distinct proteins included universal stress protein (USP), superoxide dismutase (SOD), peroxidase (POD), ferritin, and ATPase.

Dissection of the network of interactions that links RNA processing with glycolysis in the Bacillus subtilis degradosome

The RNA degradosome is a multiprotein macromolecular complex that is involved in the degradation of messenger RNA in bacteria. The composition of this complex has been found to display a high degree of evolutionary divergence, which may reflect the adaptation of species to different environments. Recently, a degradosome-like complex identified in Bacillus subtilis was found to be distinct from those found in proteobacteria, the degradosomes of which are assembled around the unstructured C-terminus of ribonuclease E, a protein not present in B. subtilis. In this report, we have investigated in vitro the binary interactions between degradosome components and have characterized interactions between glycolytic enzymes, RNA-degrading enzymes, and those that appear to link these two cellular processes. The crystal structures of the glycolytic enzymes phosphofructokinase and enolase are presented and discussed in relation to their roles in the mediation of complex protein assemblies. Taken together, these data provide valuable insights into the structure and dynamics of the RNA degradosome, a fascinating and complex macromolecular assembly that links RNA degradation with central carbon metabolism.

Direct ionization of large proteins and protein complexes by desorption electrospray ionization-mass spectrometry

Desorption electrospray ionization-mass spectrometry (DESI-MS) has advantages for rapid sample analysis with little or no sample pretreatment, but performance for large biomolecules has not been demonstrated. In this study, liquid sample DESI, an extended version of DESI used for analysis of liquid samples, was shown to have capabilities for direct ionization of large noncovalent protein complexes (>45 kDa) and proteins (up to 150 kDa). Protein complex ions (e.g., superoxide dismutase, enolase, and hemoglobin) desorbed from solution by liquid sample DESI were measured intact, indicating the capability of DESI for preserving weak noncovalent interactions. Doping the DESI spray solvent with supercharging reagents resulted in protein complex ions having increased multiple charging without complex dissociation. Ion mobility measurements of model protein cytochrome c showed that the supercharging reagent favored the more compact conformation for the lower charged protein ions. Liquid sample DESI of hydrophobic peptide gramicidin D suggests that the ionization mechanism involves a droplet pick-up mixing process. Measurement of liquid samples significantly extends the mass range of DESI-MS, allowing the analysis of high-mass proteins such as 150 kDa immunoglobulin G (IgG) and thus represents the largest protein successfully ionized by DESI to date.

Structure analysis of Entamoeba histolytica enolase

Entamoeba histolytica enolase (EhENO) reversibly interconverts 2-phosphoglyceric acid (2-PGA) and phosphoenolpyruvic acid (PEP). The crystal structure of the homodimeric EhENO is presented at a resolution of 1.9 Å. In the crystal structure EhENO presents as an asymmetric dimer with one active site in the open conformation and the other active site in the closed conformation. Interestingly, both active sites contain a copurified 2-PGA molecule. While the 2-PGA molecule in the closed active site closely resembles the conformation known from other enolase-2-PGA complexes, the conformation in the open active site is different. Here, 2-PGA is shifted approximately 1.6 Å away from metal ion I, most likely representing a precatalytic situation.

Enolase: a key player in the metabolism and a probable virulence factor of trypanosomatid parasites-perspectives for its use as a therapeutic target

Glycolysis and glyconeogenesis play crucial roles in the ATP supply and synthesis of glycoconjugates, important for the viability and virulence, respectively, of the human-pathogenic stages of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania spp. These pathways are, therefore, candidate targets for antiparasite drugs. The glycolytic/gluconeogenic enzyme enolase is generally highly conserved, with similar overall fold and identical catalytic residues in all organisms. Nonetheless, potentially important differences exist between the trypanosomatid and host enzymes, with three unique, reactive residues close to the active site of the former that might be exploited for the development of new drugs. In addition, enolase is found both in the secretome and in association with the surface of Leishmania spp. where it probably functions as plasminogen receptor, playing a role in the parasite's invasiveness and virulence, a function possibly also present in the other trypanosomatids. This location and possible function of enolase offer additional perspectives for both drug discovery and vaccination.

Molecular cloning, expression and characterization of enolase from adult Haemonchus contortus

Enolase represents a multifunctional protein involved in basic energy metabolism. In the present research, the enolase gene of Haemonchus contortus (HcENO) was cloned and characterized. Specific primers for the rapid amplification of cDNA ends (RACE) were designed based on the expression sequence tag (EST, GenBank Accession No. BF422728) to amplify the 3'- and 5'-ends of HcENO. The full length of cDNA from this gene was obtained by overlapping the sequences of 3'- and 5'-extremities and amplification by reverse transcription PCR. The biochemical activities of the recombinant protein HcENO, which was expressed in prokaryotic cells and purified by affinity chromatography, were analyzed by assays of enzymatic activity, stability to pH. The results showed that the cloned full length cDNA comprised 1583 bp and encoded a peptide with 434 amino acid residues which showed sequence similarity to several known enolases. The biochemical assay showed that the protein encoded by the HcENO exhibited enzymatic activity, whilst the HcENO was stable between pH 6 and 8. The natural enolase of H. contortus detected by immunoblot assay was approximately 49 kDa in size, and the recombinant HcENO was recognized strongly by serum from experimentally infected goats.

Mass spectrometry analysis of the post-translational modifications of alpha-enolase from pancreatic ductal adenocarcinoma cells

Enolase is a key glycolytic enzyme that catalyzes the dehydration of 2-phosphoglycerate to phosphoenolpyruvate. Recently, enolase was revealed as an important protein in pathophysiological processes since it was found on the surface of hematopoietic cells and overexpressed in several tumor cells. Our previous studies demonstrated that alpha-enolase is up-regulated in pancreatic ductal adenocarcinoma (PDAC). In this present work, we further characterized the alpha-enolase from PDAC and normal pancreatic duct cells by mass spectrometry using LTQ-Orbitrap and identified multiple post-translational modifications of alpha-enolase, such as phosphorylation, acetylation, and methylation. The result showed that more acetylated lysines, methylated aspartic acids, and glutamic acids were found in PDAC cells than that of normal pancreatic duct cells.

cDNA cloning and expression pattern of two enolase genes from the Chinese oak silkworm, Antheraea pernyi

In this study, two enolase genes were isolated and characterized from the Chinese oak silkworm, Antheraea perny, which were designated as enolase I and II, respectively. The enolase I cDNA sequence was 1712 bp with an open reading frame (ORF) of 1302 bp encoding 433 amino acids. The enolase II cDNA sequence was 1549 bp with an ORF of 1296 bp encoding 431 amino acids. The amino acid sequences of the two genes share several conserved features/sites of enolase. Antheraea pernyi enolase I shows 93%-97% sequence identity to enolases of lepidopterans available to date, 75%-82% identity to enolases of other invertebrates, 60%-72% identity to enolases of other organisms including vertebrates, plants, and fungi. Antheraea pernyi enolase II shows 84% identity to Bombyx mori enolase II, but 60% identity to A. pernyi enolase I. In the phylogenetic tree, enolase II sequences from A. pernyi and B. mori were clearly separated from the majority of enolase sequences of higher organisms including A. pernyi and B. mori enolase I sequences. By sequence comparisons and phylogenetic analysis, we suggest that enolase II from A. pernyi and B. mori may be a new member of the enolase superfamily. Antheraea pernyi enolase I mRNA was found in all tested tissues whereas enolase II mRNA was expressed specifically in the spermaries and ovaries, suggesting that the product of enolase II gene may be related to reproduction. The transcript abundance of A. pernyi enolase I gene was significantly down-regulated after cold shock and significantly up-regulated after heat shock, suggesting that A. pernyi enolase I gene may be inducible by temperature stress.

Engineering the enolase magnesium II binding site: implications for its evolution

The glycolytic enzyme enolase catalyzes the reversible elimination of water from 2-phosphoglycerate (2-PGA) to form phosphoenolpyruvate (PEP). Two magnesium ions in the active site are thought to facilitate the reaction by activation of the C2 proton of 2-PGA and charge stabilization of the intermediate. The initial abstraction of a proton from a carboxylic acid is common to all members of the enolase superfamily, yet in all other known members of this superfamily, only one magnesium ion (MgI) per active site is sufficient to promote catalysis. We wanted to further investigate the importance of the second magnesium ion (MgII) for the catalytic mechanism of yeast enolase 1. Toward this end, we removed all MgII coordinating residues and replaced substrate-MgII interactions by introducing positively charged side chains. High-resolution crystal structures and activity assays show that the introduced positively charged side chains effectively prohibit MgII binding but fail to promote catalysis. We conclude that enolase is inactive without MgII, yet control mutants without additional positively charged side chains retain basal enolase activity through binding of magnesium to 2-PGA in an open active site without the help of MgII coordinating residues. Thus, we believe that ancestral enolase activity might have evolved in a member of the enolase superfamily that provides only the necessary catalytic residues and the binding site for MgI. Additionally, precatalytic binding of 2-PGA to the apo state of enolase was observed.

Aphidius ervi teratocytes release an extracellular enolase

We report the cloning of a gene and the characterization of the encoded protein, which is released by the teratocytes of the parasitoid Aphidius ervi in the haemocoel of the host aphid Acyrthosiphon pisum. The studied protein was identified by LC-MS/MS, and the gathered information used for isolating the full length cDNA. The corresponding gene was made of 3 exons and 2 introns, and was highly expressed in the adult wasps and in parasitized hosts. The translation product, which was named Ae-ENO, showed a very high level of sequence identity with insect enolases. In vivo immunodetection experiments evidenced Ae-ENO localization in round spots, present in the teratocytes and released in the host haemocoel. Moreover, strong immunoreactivity was detected on the surface of A. ervi larvae and of host embryos. Ae-ENO expressed in insect cells was not secreted in the medium, indicating the occurrence in the teratocytes of an unknown pathway for Ae-ENO release. The recombinant protein produced in bacteria under native conditions was a dimer, with evident enolase activity (K(m) = 0.086 +/- 0.017 mM). Enolase is a well known enzyme in cell metabolism, which, however, is associated with a multifunctional role in disease, when present in the extracellular environment, on the surface of prokaryotic and eukaryotic cells. In these cases, the enolase mediates the activation of enzymes involved in the invasion of tissues by pathogens and tumour cells, and in the evasion of host immune response. The possible role played by Ae-ENO in the host regulation process is discussed in the light of this information.

Effect of deletion of a plant like pentapeptide insert on kinetic, structural and immunological properties of enolase from Plasmodium falciparum

Plasmodium falciparum enolase (Pfen) is of photosynthetic lineage as evident from the presence of a plant like pentapeptide insert (104)EWGWS(108) in a highly conserved surface loop of the protein. Such a unique region which is absent in human enolase, constitutes an excellent target for inhibitor design, provided its essentiality for function could be demonstrated. A deletion Pfen lacking this insert was made and the effect of this deletion on activity and structure was assessed. Deletion of insert resulted in approximately 100-fold decrease in k(cat)/K(m) and caused dissociation of dimeric form into monomers. Since the parasite enolase localizes on the merozoite surface and confers partial protection against malaria [I. Pal-Bhowmick, M. Mehta, I. Coppens, S. Sharma, G.K. Jarori, Infect. Immun. 75(11) (2007) 5500-5008], the possibility of the insert being involved in protective response was examined. Serum from Pfen vaccinated mouse which showed prolonged survival to parasite challenge had negligible reactivity against deletion protein as compared to wild type enolase. These results indicate that the insert sequence is required for the full enolase activity and may constitute the protective antigenic epitope in parasite enolase.

Crystallization and preliminary X-ray analysis of human liver alpha-enolase

Enolase is a multifunctional enzyme that plays important roles in many biological and disease processes. alpha-Enolase from human liver (hENO1) was expressed as a soluble protein and purified by affinity column chromatography and gel filtration. Crystals were obtained by the hanging-drop vapour-diffusion method and diffracted to 2.5 A resolution. The crystals belonged to space group P2(1), with unit-cell parameters a = 72.85, b = 66.02, c = 79.43 A, beta = 94.54 degrees .