Cloning, expression, and purification of fumarase from the parasitic nematode Ascaris suum

Immunoproteomics and Surfaceomics of the Adult Tapeworm Hymenolepis diminuta

In cestodiasis, mechanical and molecular contact between the parasite and the host activates the immune response of the host and may result in inflammatory processes, leading to ulceration and intestinal dysfunctions. The aim of the present study was to identify antigenic proteins of the adult cestode Hymenolepis diminuta by subjecting the total protein extracts from adult tapeworms to 2DE immunoblotting (two-dimensional electrophoresis combined with immunoblotting) using sera collected from experimentally infected rats. A total of 36 protein spots cross-reacting with the rat sera were identified using LC-MS/MS. As a result, 68 proteins, including certain structural muscle proteins (actin, myosin, and paramyosin) and moonlighters (heat shock proteins, kinases, phosphatases, and glycolytic enzymes) were identified; most of these were predicted to possess binding and/or catalytic activity required in various metabolic and cellular processes, and reported here as potential antigens of the adult cestode for the first time. As several of these antigens can also be found at the cell surface, the surface-associated proteins were extracted and subjected to in-solution digestion for LC-MS/MS identification (surfaceomics). As a result, a total of 76 proteins were identified, from which 31 proteins, based on 2DE immunoblotting, were predicted to be immunogenic. These included structural proteins actin, myosin and tubulin as well as certain moonlighting proteins (heat-shock chaperones) while enzymes with diverse catalytic activities were found as the most dominating group of proteins. In conclusion, the present study shed new light into the complexity of the enteric cestodiasis by showing that the H. diminuta somatic proteins exposed to the host possess immunomodulatory functions, and that the immune response of the host could be stimulated by diverse mechanisms, involving also those triggering protein export via yet unknown pathways.

Enhancing the thermostability of fumarase C from Corynebacterium glutamicum via molecular modification

Fumarases have been successfully applied in industry for the production of l-malate. However, the industrialization of fumarases is limited by their low thermostability. In this study, the thermostability of fumarase C from Corynebacterium glutamicum was enhanced through directed evolution, simulated mutagenesis, site-directed mutagenesis and saturated mutagenesis. Mutant 2G (A411V) was initially constructed through directed evolution. Its half-life at 50 °C (t_1/2, _50°C) increased from 1 min to 2.2 min, and the T₅₀¹⁵ (temperature at which the activity of enzyme decreased by 50% in 15 min) increased from 44.8 °C to 47.2 °C. Besides, several different mutants were obtained by site-directed mutation. Among them, mutant 3G (A227V) showed significant improvement in thermostability with a 3.3-fold improvement of t_1/2, _50°C and a 3.6 °C increase in T₅₀¹⁵ compared to the wild-type enzyme. Then, 2/3G (A227V, A411V) was obtained by combining the mutant 2G with the mutant 3G, for which the t_1/2, _50°C and T₅₀¹⁵ increased to more than 768 min and 52.4 °C, respectively. Finally, site-saturated mutagenesis was employed on amino acid residues 175-Glu, 228-Gly, 297-Gly, 320-Lys and 464-Glu to maximize the thermostability of mutant 2/3G. The most thermostable mutant 175G with amino acid substitutions (A227V, A411V, E175K) was isolated. Its t_1/2,50°C increased to more than 2700 min while that of wild-type enzyme was only 1 min and T₅₀¹⁵ was 9.8 °C higher than the wild-type enzyme. The thermostable mutated enzymes generated without affecting the activity in this study would be an attractive candidate for industrial applications.

Comparative Proteomic Analysis of Hymenolepis diminuta Cysticercoid and Adult Stages

Cestodiases are common parasitic diseases of animals and humans. As cestodes have complex lifecycles, hexacanth larvae, metacestodes (including cysticercoids), and adults produce proteins allowing them to establish invasion and to survive in the hostile environment of the host. Hymenolepis diminuta is the most commonly used model cestode in experimental parasitology. The aims of the present study were to perform a comparative proteomic analysis of two consecutive developmental stages of H. diminuta (cysticercoid and adult) and to distinguish proteins which might be characteristic for each of the stages from those shared by both stages. Somatic proteins of H. diminuta were isolated from 6-week-old cysticercoids and adult tapeworms. Cysticercoids were obtained from experimentally infected beetles, Tenebrio molitor, whereas adult worms were collected from experimentally infected rats. Proteins were separated by GeLC-MS/MS (one dimensional gel electrophoresis coupled with liquid chromatography and tandem mass spectrometry). Additionally protein samples were digested in-liquid and identified by LC-MS/MS. The identified proteins were classified according to molecular function, cellular components and biological processes. Our study showed a number of differences and similarities in the protein profiles of cysticercoids and adults; 233 cysticercoid and 182 adult proteins were identified. From these proteins, 131 were present only in the cysticercoid and 80 only in the adult stage samples. Both developmental stages shared 102 proteins; among which six represented immunomodulators and one is a potential drug target. In-liquid digestion and LC-MS/MS complemented and confirmed some of the GeLC-MS/MS identifications. Possible roles and functions of proteins identified with both proteomic approaches are discussed.

Identification and characterization of a novel fumarase gene by metagenome expression cloning from marine microorganisms

BACKGROUND

Fumarase catalyzes the reversible hydration of fumarate to L-malate and is a key enzyme in the tricarboxylic acid (TCA) cycle and in amino acid metabolism. Fumarase is also used for the industrial production of L-malate from the substrate fumarate. Thermostable and high-activity fumarases from organisms that inhabit extreme environments may have great potential in industry, biotechnology, and basic research. The marine environment is highly complex and considered one of the main reservoirs of microbial diversity on the planet. However, most of the microorganisms are inaccessible in nature and are not easily cultivated in the laboratory. Metagenomic approaches provide a powerful tool to isolate and identify enzymes with novel biocatalytic activities for various biotechnological applications.

RESULTS

A plasmid metagenomic library was constructed from uncultivated marine microorganisms within marine water samples. Through sequence-based screening of the DNA library, a gene encoding a novel fumarase (named FumF) was isolated. Amino acid sequence analysis revealed that the FumF protein shared the greatest homology with Class II fumarate hydratases from Bacteroides sp. 2_1_33B and Parabacteroides distasonis ATCC 8503 (26% identical and 43% similar). The putative fumarase gene was subcloned into pETBlue-2 vector and expressed in E. coli BL21(DE3)pLysS. The recombinant protein was purified to homogeneity. Functional characterization by high performance liquid chromatography confirmed that the recombinant FumF protein catalyzed the hydration of fumarate to form L-malate. The maximum activity for FumF protein occurred at pH 8.5 and 55°C in 5 mM Mg(2+). The enzyme showed higher affinity and catalytic efficiency under optimal reaction conditions: K(m) = 0.48 mM, V(max) = 827 μM/min/mg, and k(cat)/K(m) = 1900 mM/s.

CONCLUSIONS

We isolated a novel fumarase gene, fumF, from a sequence-based screen of a plasmid metagenomic library from uncultivated marine microorganisms. The properties of FumF protein may be ideal for the industrial production of L-malate under higher temperature conditions. The identification of FumF underscores the potential of marine metagenome screening for novel biomolecules.

In-gel activity staining of oxidized nicotinamide adenine dinucleotide kinase by blue native polyacrylamide gel electrophoresis

Oxidized nicotinamide adenine dinucleotide (NAD(+)) kinase (NADK, E.C. 2.7.1.23) plays an instrumental role in cellular metabolism. Here we report on a blue native polyacrylamide gel electrophoretic technique that allows the facile detection of this enzyme. The product, oxidized nicotinamide adenine dinucleotide phosphate (NADP(+)), formed following the reaction of NADK with NAD(+) and adenosine 5'-triphosphate was detected with the aid of glucose-6-phosphate dehydrogenase or NADP(+)-isocitrate dehydrogenase, iodonitrotetrazolium chloride, and phenazine methosulfate. The bands at the respective activity sites were excised and subjected to native and denaturing two-dimensional electrophoresis for the determination of protein levels. Hence this novel electrophoretic method allows the easy detection of NADK, a critical enzyme involved in pyridine homeostasis. Furthermore, this technique allowed the monitoring of the activity and expression of this kinase in various biological systems.

Gene expression profiles associated with the transition to parasitism in Ancylostoma caninum larvae

Ancylostoma caninum is a common canine parasite responsible for anemia and death in infected dogs. Gene expression profiling was used to investigate molecular differences between two different forms of the third larval stage (L3s): infective free-living larvae and in vitro serum-stimulated larvae that mimic the initial stages of parasitism of a host. We developed an A. caninum cDNA microarray consisting of 4191 EST clones, and used it to identify a set of 113 genes that are differentially regulated between infective and parasitic larval stages. Real-time RT-PCR was used to confirm the expression differences of a subset of the genes. Of the genes repressed upon serum stimulation, seven encode members of the 'Ancylostoma secreted protein' ASP family, while another transcript encoding a 24 kDa excretory protein with similarity to ASP was up-regulated in serum-stimulated L3s. This suggests that different members of a protein family that has important implications for the hookworm's parasitic lifestyle are regulated in a complementary manner in response to serum stimulation. Comparison of two strains of A. caninum from North Carolina and Maryland only identified a single gene, one of the members of the ASP family, that was differentially repressed upon serum stimulation.

Molecular cloning and functional characterization of fumarases C in Neisseria species

Fumarase is one of the key enzymes in the TCA cycle and has been implicated in virulence and survival of some microorganisms under suboptimal environmental conditions. In this study, the fumC genes that encode fumarase C (FUMCs) from Neisseria meningitidis, N. gonorrhoeae and N. subflava were identified by homology-based analysis, cloned by polymerase chain reactions and fully sequenced. The inferred primary sequence of neisserial FUMCs showed a high degree of conservation with 97.8-98.7% amino acid identity. However, phylogenetic analysis revealed that these neisserial FUMCs are divergent from class II fumarases found in other microorganisms, rat and human. The putative fumC genes were subcloned into the expression vector, pGEX-6P-1 and efficiently expressed in Esherichia coli BL21. The purified recombinant fusion proteins obtained by affinity chromatography demonstrated high catalytic activities (120-180 U/mg), thus authenticating the identities and functionalities of the cloned genes. Whether FUMC has any physiological relevance to the pathogenesisity of Neisseriae must await future gene disruption or mutagenesis studies.

Blue native polyacrylamide gel electrophoresis and the monitoring of malate- and oxaloacetate-producing enzymes

We demonstrate a facile blue native polyacrylamide gel electrophoresis (BN-PAGE) technique to detect two malate-generating enzymes, namely fumarase (FUM), malate synthase (MS) and four oxaloacetate-forming enzymes, namely pyruvate carboxylase (PC), phosphoenolpyruvate carboxykinase (PEPCK), citrate lyase (CL) and aspartate aminotransferase (AST). Malate dehydrogenase (MDH) was utilized as a coupling enzyme to detect either malate or oxaloacetate in the presence of their respective substrates and cofactors. The latter four oxaloacetate-forming enzymes were identified by 2,6-dichloroindophenol (DCIP) and p-iodonitrotetrazolium (INT) while the former two malate-producing enzymes were visualized by INT and phenazine methosulfate (PMS) in the reaction mixtures, respectively. The band formed at the site of enzymatic activity was easily quantified, while Coomassie staining provided information on the protein concentration. Hence, the expression and the activity of these enzymes can be readily evaluated. A two-dimensional (2D) BN-PAGE or SDS-PAGE enabled the rapid purification of the enzyme of interest. This technique also provides a quick and inexpensive means of quantifying these enzymatic activities in normal and stressed biological systems.