pET Expression System Research Articles

Vaccination with a cocktail of Ancylostoma ceylanicum recombinant antigens leads to worm burden reduction in hamsters

Hookworms, a group to which Ancylostoma ceylanicum belongs, are gastrointestinal nematodes that infect more than 700 million people around the world. They are a leading cause of anemia in developing countries. In order to effectively prevent hookworm infections research is conducted to develop an effective vaccine using recombinant antigens of the parasite. The aim of this study was to examine the influence of the hosts' on protection against ancylostomiasis and the shaping of the humoral immune response among Syrian hamsters after immunization with a cocktail of five A. ceylanicum recombinant antigens. Ace-ASP-3, Ace-ASP-4, Ace-APR-1, Ace-MEP-6 and Ace-MEP-7 were obtained in the pET expression system. Immunization with a vaccine cocktail resulted in a 33.5% worm burden reduction. The immunogenicity of the recombinant proteins were determined using ELISA. Statistical analysis showed that vaccinated hamsters developed stronger humoral responses to four of five recombinant antigens (the exception being Ace-ASP-3) compared to hamsters from the control group.

Subunit Protein Vaccine Delivery System for Tuberculosis Based on Hepatitis B Virus Core VLP (HBc-VLP) Particles.

Despite the development of modern medicine, tuberculosis (TB), caused by the pathogenic bacterium, Mycobacterium tuberculosis (Mtb), remains one of the deadliest diseases. This bacterium can lay dormant in individuals and get activated when immunity goes down and has also shown considerable prowess in mutating into drug resistant forms. The global emergence of such drug resistant Mtb and the lack of efficacy of Bacille Calmette Guérin (BCG), the only vaccine available so far, have resulted in a situation which cries out for a safe and effective tuberculosis vaccine.Number of different strategies has been used for developing new anti-TB vaccines and several protective antigens have been identified so far. One strategy, the use of protein subunits, has the potential to develop into a powerful tuberculosis vaccine, not only because of its efficacy and safety, but also because they are economical. The proper delivery of protein subunit vaccines with adjuvants or novel delivery systems is necessary for inducing protective immune responses. The available adjuvants or delivery systems are inadequate for generating such a response. In the present method, we have constructed a vaccine delivery system for tuberculosis based on Virus-Like Particles (VLPs). Hepatitis B Virus core antigen gene was recombinantly modified using Overlap Extension PCR (OEPCR). The final construct was designed to express HBc-VLP carrying external antigen (fusion VLP). Mycobacterium tuberculosis antigen CFP-10 was used for the construction of fusion VLP. The recombinant gene for the construct was cloned into a pET expression system and transformed into E. coli BL21(DE3) and induced with IPTG to express the protein. The fusion protein was purified using the Histidine tag and allowed to form VLPs. The preformed VLPs were purified by sucrose density gradient centrifugation. The VLPs were characterized using Transmission Electron Microscopy (TEM).

Generation of GFP Native Protein for Detection of Its Intracellular Uptake by Cell-Penetrating Peptides

Different types of lipid- and polymer-based vectors have been developed to deliver proteins into cells, but these methods showed relatively poor efficiency. Recently, a group of short, highly basic peptides known as cell-penetrating peptides (CPPs) were used to carry polypeptides and proteins into cells. In this study, expression and purification of GFP protein was performed using the prokaryotic pET expression system. We used two amphipathic CPPs (Pep-1 and CADY-2) as a novel delivery system to transfer the GFP protein into cells. The morphological features of the CPP/GFP complexes were studied by scanning electron microscopy (SEM), Zetasizer, and SDS-PAGE. The efficiency of GFP transfection using Pep-1 and CADY-2 peptides and TurboFect reagent was compared with FITC-antibody protein control delivered by these transfection vehicles in the HEK-293T cell line. SEM data confirmed formation of discrete nanoparticles with a diameter of below 300 nm. Moreover, formation of the complexes was detected using SDS-PAGE as two individual bands, indicating non-covalent interaction. The size and homogeneity of Pep-1/GFP and CADY-2/GFP complexes were dependent on the ratio of peptide/cargo formulations, and responsible for their biological efficiency. The cells transfected by Pep-1/GFP and CADY-2/GFP complexes at a molar ratio of 20 : 1 demonstrated spreading green regions using fluorescent microscopy. Flow cytometry results showed that the transfection efficiency of Pep-based nanoparticles was similar to CADY-based nanoparticles and comparable with TurboFect-protein complexes. These data open an efficient way for future therapeutic purposes.

Recognition of Linear B-Cell Epitope of Betanodavirus Coat Protein by RG-M18 Neutralizing mAB Inhibits Giant Grouper Nervous Necrosis Virus (GGNNV) Infection.

Betanodavirus is a causative agent of viral nervous necrosis syndrome in many important aquaculture marine fish larvae, resulting in high global mortality. The coat protein of Betanodavirus is the sole structural protein, and it can assemble the virion particle by itself. In this study, we used a high-titer neutralizing mAB, RG-M18, to identify the linear B-cell epitope on the viral coat protein. By mapping a series of recombinant proteins generated using the E. coli PET expression system, we demonstrated that the linear epitope recognized by RG-M18 is located at the C-terminus of the coat protein, between amino acid residues 195 and 338. To define the minimal epitope region, a set of overlapping peptides were synthesized and evaluated for RG-M18 binding. Such analysis identified the 195VNVSVLCR202 motif as the minimal epitope. Comparative analysis of Alanine scanning mutagenesis with dot-blotting and ELISA revealed that Valine197, Valine199, and Cysteine201 are critical for antibody binding. Substitution of Leucine200 in the RGNNV, BFNNV, and TPNNV genotypes with Methionine200 (thereby simulating the SJNNV genotype) did not affect binding affinity, implying that RG-M18 can recognize all genotypes of Betanodaviruses. In competition experiments, synthetic multiple antigen peptides of this epitope dramatically suppressed giant grouper nervous necrosis virus (GGNNV) propagation in grouper brain cells. The data provide new insights into the protective mechanism of this neutralizing mAB, with broader implications for Betanodavirus vaccinology and antiviral peptide drug development.

Abstract 2276: Induction of apoptosis and inhibition of angiogenesis by novel fusion protein - AD-O54.9 as a new preclinical strategy in cancer treatment

Abstract Background For almost two decades tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo2L) has been under extensive development as a potential therapeutic agent. TRAIL/Apo2L is a member of the TNF superfamily with unique ability to induce apoptosis in cancer cells while remaining neutral to normal cells. Tumor growth is tightly related to new blood vessel formation and tissue remodeling. Platelet derived growth factor (PDGF) is important in vascular physiological and pathological development. Inhibition of PDGF pathway blocks angiogenesis what results in reduction of tumor growth. We proposed a novel fusion protein (AD-O54.9) with dualistic proapoptotic and antiangiogenic activity. Our molecule consists of the soluble recombinant TRAIL/Apo2L variant linked with an effector peptide sequence and an activation motif recognized by tumor-specific proteases (MMPs, uPa) between. The effector peptide is composed of 19-amino acid fragment derived from human PDGF, which binds the PDGF receptors competitively to the natural ligand while being itself devoid of activity. As a consequence, angiogenic activity of PDGF is blocked, stimulation of new blood vessels formation does not occur and finally tumor growth is inhibited. Materials and methods AD-O54.9 protein was expressed in E. coli, using pET expression system, and purified by IEC chromatography. Cytotoxic activity of AD-O54.9 was examined using a propidium iodide assay and its antiangiogenic activity was evaluated by HUVEC tube formation and ring aortic assays. Safety was tested on human primary hepatocytes. The proapoptotic and antiproliferative activity was tested using molecular biology and flow cytometry methods. In vivo potential was examined on mice xenograft models of human colorectal adenocarcinoma (Colo205), human lung carcinoma (NCI-H460-luc2), human pancreatic carcinoma (MIA PaCa-2) and human oesophageal adenocarcinoma (OE19) cell lines where molecules showed anticancer activity. Results The molecule showed in vitro specific cytotoxic effect on various primary cancer cell lines at IC50 below 0.01 ng/ml. We demonstrated that AD-O54.9 is a very potent apoptosis inducer and inhibitor of angiogenesis. This fusion protein showed superior efficacy displaying significant tumor volume regression compared with TRAIL/Apo2L and standard chemotherapeutic agents. Conclusions The obtained results confirm that we developed a very promising fusion molecule with a high potential of anticancer activity that could be considered as a novel therapeutic agent. Citation Format: Piotr Rózga, Jerzy Pieczykolan, Bartłomiej Zerek, Anna Pieczykolan, Marlena Gałązka, Katarzyna Bukato, Michał Szymanik, Albert Jaworski, Sebastian Pawlak, Małgorzata Teska-Kamińska, Anna Grochot-Przęczek. Induction of apoptosis and inhibition of angiogenesis by novel fusion protein - AD-O54.9 as a new preclinical strategy in cancer treatment. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2276. doi:10.1158/1538-7445.AM2014-2276

A dps promoter based expression system for improved solubility of expressed proteins in Escherichia coli

Escherichia coli is widely used for recombinant protein production due to its well established genetic manipulation techniques and cost effectiveness of the associated production processes. Soluble expression of heterologous recombinant proteins constitutes a major problem in the deployment of bacterial expression systems. We have developed a dps promoter based expression system in E. coli for improved solubility of expressed proteins. The resulting expression system was found to be superior to the IPTG inducible T7 promoter based pET expression system for production of soluble β-galactosidase, tdTomato, and mCherry. The dps promoter based expression system was shown to be functional in most commonly used strains of E. coli without need for prior genetic manipulation of the host genome.

Molecular cloning and characterization of a lysozyme cDNA from the mole cricket Gryllotalpa orientalis (Orthoptera: Gryllotalpidae).

A full-length lysozyme cDNA from Gryllotalpa orientalis was cloned and sequenced. The deduced amino acid sequence of the lysozyme protein was 143 amino acids in length, with a calculated molecular mass of 15.84 kDa and an isoelectric point of 4.74. Sequence motifs, together with alignment and phylogenetic results, confirmed that G. orientalis lysozyme belongs to the C (chicken)-type lysozyme family of proteins. The protein sequence of lysozyme from G. orientalis showed high identity to that of Drosophila melanogaster (51.7 %); however, in contrast to D. melanogaster lysozyme, G. orientalis lysozyme was immune inducible and expressed in a wide range of tissues. Expression of G. orientalis lysozyme mRNA was highest at 8 h post-infection and subsequently decreased with time after bacterial infection. We also expressed G. orientalis lysozyme protein in vitro using the pET expression system. Compared with the negative control, over-expressed G. orientalis lysozyme showed antimicrobial activity against Gram-negative bacteria Escherichia coli and Gram-positive bacteria Bacillus subtilis by radial diffusion assay, with minimal inhibitory concentration values of 30.3 and 7.55 µM, respectively. These results indicate that G. orientalis lysozyme may have stronger antimicrobial activity than other lysozymes against a broad range of microorganisms.

Characterization of a biocatalyst catalyzing biotransformation of highly branched fatty acids

Abstract Highly branched fatty acids are of particular interest as they have polyketide-like structures with several chiral centers and regioselective fictionalization of such substances would offer convenient routes to new important pharmaceutical compounds. A novel biocatalyst from Bacillus cereus was cloned and expressed in Escherichia coli BL21 using pET expression system. It can be easily expressed in E. coli with a high yield. The expressed recombinant enzyme was purified by Ni-NTA affinity chromatography and characterized. We elucidated that this enzyme catalyzes the oxidation of alkanoic acids (C8 to C17) and unsaturated fatty acids (C18). Substrate binding study showed the tightest binding fatty acid was myristic acid (C14), yielding a K d value of 7.88 µM. This biocatalyst showed the activity of saturated fatty acids of shorter (C8, C10), which could not be observed from other enzyme.

Metabolic changes of recombinant Escherichia coli BL21 (DE3) during overexpression of recombinant human interferon beta in HCDC

The influence of the overexpression of recombinant human interferon beta (rhINF-β) during high cell density cultivation (HCDC) on metabolic characteristics of recombinant E. coli BL21 (DE3) was studied. Fed-batch culture technique was employed to grow the host cell for the production of human interferon beta in pET expression system in a 5L bench-top bioreactor. The final cell density of 42.15 g L-1 and cell growth (OD600nm) of 103.5 were obtained respectively in fed-batch culture experiment. Four hours after the induction, the specific growth rate was decreased. The initial concentration of the glucose, ammonium and phosphate in the TB culture medium were 5.0, 12.0 and 3.12 g L-1 respectively. The maximum amount of the produced rhINF-β was 2.8 g L-1 after applying the fed-batch cultivation technique. Besides, time profiles of the acetate and lactate production were similar, the acetate concentration (4.91 g L -1 ) was lower than that of lactate (10.08 g L -1 ) and the

Cloning, expression and characterization of a lipase encoding gene from human oral metagenome.

The human oral metagenomic DNA cloned into plasmid pUC19 was used to construct a DNA library in Escherichia coli. Functional screening of 40,000 metagenomic clones led to identification of a clone LIP2 that exhibited halo on tributyrin agar plate. Sequence analysis of LIP2 insert DNA revealed a 939bp ORF (omlip1) which showed homology to lipase 1 of Acinetobacter junii SH205. The omlip1 ORF was cloned and expressed in E. coli BL21 (DE3) using pET expression system. The recombinant enzyme was purified to homogeneity and the biochemical properties were studied. The purified OMLip1 hydrolyzed p-nitrophenyl esters and triacylglycerol esters of medium and long chain fatty acids, indicating the enzyme is a true lipase. The purified protein exhibited a pH and temperature optima of 7 and 37°C respectively. The lipase was found to be stable at pH range of 6-7 and at temperatures lower than 40°C. Importantly, the enzyme activity was unaltered, by the presence or absence of many divalent cations. The metal ion insensitivity of OMLip1offers its potential use in industrial processes.

Cloning and expression of dnaK gene from Bacillus pumilus of hot water spring origin

A set of thermotolerant strains isolated from hot springs of Manikaran and Bakreshwar (India) were selected with an aim to isolate dnak gene which encodes DnaK protein. The gene dnaK along with its flanking region was successfully amplified from 5 different strains (4 from Bakreshwar and one from Manikaran). Restriction fragment length polymorphism (RFLP) revealed that amplicons were almost identical in sequence. The dnak gene from one representative, Bacillus pumilus strain B3 isolated from Bakreshwar hot springs was successfully cloned and sequenced. The dnaK gene was flanked by gene grpE on one side. The dnaK gene was 1842bp in length encoding a polypeptide of 613 amino acid residues. Calculated molecular weight and pI of the protein were 66,128.36Da and 4.72 respectively. The deduced amino acid sequence of this gene shared high sequence homology with other DnaK proteins and its homologue Hsp 70 from other microorganisms, but possessed 36 substitutions and two insertions, as compared to DnaK protein of Bacillus subtilis. The dnaK gene of B. pumilus was successfully expressed in Escherichia coli BL 21 (DE3) using pET expression systems. Heterologous expression of dnaK of B. pumilus in E. coli BL 21 (DE3) allowed for the growth of E. coli up to 50°C and survival up to 60°C for 16h, suggesting that dnak from B. pumilus imparts tolerance to host cells under high temperature. This novel gene can be an important component for possible utilization in abiotic stress management of plants.

A novel feruloyl esterase from a soil metagenomic library with tannase activity

Abstract A gene (tan410) encoding a feruloyl esterase was isolated by screening a cotton soil metagenomic library. Sequence analysis revealed that tan410 encodes a protein of 520 amino acids with a predicted molecular weight of 55 kDa. The gene was further expressed in Escherichia coli BL21 (DE3) using a pET expression system. The recombinant enzyme was purified and characterized. Its optimum temperature and pH were 35 °C and 7.0, respectively. Tan410 activity was enhanced by the addition of Mn2+, Mg2+, NH4+ and Ni2+. Besides ethyl ferulate, methyl caffeate, and methyl p-coumarate, Tan410 can also hydrolyze methyl gallate, tannic acid, epicatechin gallate, and epigallocatechin gallate which makes Tan410 an interesting enzyme for biotechnological applications.

Molecular cloning of a novel bioH gene from an environmental metagenome encoding a carboxylesterase with exceptional tolerance to organic solvents

BackgroundBioH is one of the key enzymes to produce the precursor pimeloyl-ACP to initiate biotin biosynthesis de novo in bacteria. To date, very few bioH genes have been characterized. In this study, we cloned and identified a novel bioH gene, bioHx, from an environmental metagenome by a functional metagenomic approach. The bioHx gene, encoding an enzyme that is capable of hydrolysis of p-nitrophenyl esters of fatty acids, was expressed in Escherichia coli BL21 using the pET expression system. The biochemical property of the purified BioHx protein was also investigated.ResultsScreening of an unamplified metagenomic library with a tributyrin-containing medium led to the isolation of a clone exhibiting lipolytic activity. This clone carried a 4,570-bp DNA fragment encoding for six genes, designated bioF, bioHx, fabG, bioC, orf5 and sdh, four of which were implicated in the de novo biotin biosynthesis. The bioHx gene encodes a protein of 259 aa with a calculated molecular mass of 28.60 kDa, displaying 24-39% amino acid sequence identity to a few characterized bacterial BioH enzymes. It contains a pentapeptide motif (Gly76-Trp77-Ser78-Met79-Gly80) and a catalytic triad (Ser78-His230-Asp202), both of which are characteristic for lipolytic enzymes. BioHx was expressed as a recombinant protein and characterized. The purified BioHx protein displayed carboxylesterase activity, and it was most active on p-nitrophenyl esters of fatty acids substrate with a short acyl chain (C4). Comparing BioHx with other known BioH proteins revealed interesting diversity in their sensitivity to ionic and nonionic detergents and organic solvents, and BioHx exhibited exceptional resistance to organic solvents, being the most tolerant one amongst all known BioH enzymes. This ascribed BioHx as a novel carboxylesterase with a strong potential in industrial applications.ConclusionsThis study constituted the first investigation of a novel bioHx gene in a biotin biosynthetic gene cluster cloned from an environmental metagenome. The bioHx gene was successfully cloned, expressed and characterized. The results demonstrated that BioHx is a novel carboxylesterase, displaying distinct biochemical properties with strong application potential in industry. Our results also provided the evidence for the effectiveness of functional metagenomic approach for identifying novel bioH genes from complex ecosystem.

A novel O-methyltransferase involved in the first methylation step of yatein biosynthesis from matairesinol in Anthriscus sylvestris

Yatein is an important biosynthetic precursor of the lignan podophyllotoxin. In Anthriscus sylvestris, yatein biosynthesis is preceded by two regioselective methylations involving the intermediates: thujaplicatin and 5-O-methylthujaplicatin. The two methylation steps are most likely catalyzed by plant O-methyltransferases (OMTs). In this paper, we report the isolation and characterization of a cDNA encoding an OMT involved in the first methylation step. The OMT cDNA was isolated from an A. sylvestris cDNA library prepared from roots and young shoots. The OMT was expressed as a recombinant protein using the pET expression system. Of the substrates that were tested, the recombinant OMT exclusively catalyzed regioselective methylation of thujaplicatin to produce 5-O-methylthujaplicatin, and thus was designated as A. sylvestris thujaplicatin OMT (AsTJOMT). Kinetic analysis with its substrate (thujaplicatin) showed that AsTJOMT had a Km value of 3.8 µM and kcat value of 0.29 min−1. Quantitative real-time polymerase chain reaction showed that AsTJOMT had the highest expression level in roots compared with other organs. This was in accordance with plant protein assays in which specific activity for thujaplicatin was significantly higher in roots compared with other organs. To the best of our knowledge, this is the first report on the isolation and characterization of a thujaplicatin-specific plant OMT.

Periplasmic production via the pET expression system of soluble, bioactive human growth hormone

A pET based expression system for the production of recombinant human growth hormone (hGH) directed to the Escherichia coli periplasmic space was developed. The pET22b plasmid was used as a template for creating vectors that encode hGH fused to either a pelB or ompA secretion signal under control of the strong bacteriophage T7 promoter. The pelB- and ompA-hGH constructs expressed in BL21 (λDE3)-RIPL E. coli are secreted into the periplasm which facilitates isolation of soluble hGH by selective disruption of the outer membrane. A carboxy-terminal poly-histidine tag enabled purification by Ni2+ affinity chromatography with an average yield of 1.4mg/L culture of purified hGH, independent of secretion signal. Purified pelB- and ompA-hGH are monomeric based on size exclusion chromatography with an intact mass corresponding to mature hGH indicating proper cleavage of the signal peptide and folding in the periplasm. Both pelB- and ompA-hGH bind the hGH receptor with high affinity and potently stimulate Nb2 cell growth. These results demonstrate that the pET expression system is suitable for the rapid and simple isolation of bioactive, soluble hGH from E. coli.

Identification of a Novel Antifungal Peptide with Chitin-Binding Property from Marine Metagenome

A novel antifungal peptide with 36 amino acids was identified by functional screening of a marine metagenomic library. The peptide did not show similarity with any existing antimicrobial peptide sequences in the databank. The108 bp ORF designated as mmgp1 was cloned and expressed in Escherichia coli BL21 (DE3) using pET expression system. Mass spectrometry analysis of the purified recombinant peptide revealed a molecular mass of 5026.9 Da. The purified recombinant peptide inhibited the growth of Candida albicans and Aspergillus niger. The peptide was predicted to adopt α- helical conformation with an extended coil containing a ligand binding site for N-acetyl-D-glucosamine. The α- helicity of the peptide was demonstrated by circular dichroism spectroscopy in the presence of chitin or membrane mimicking solvent, trifluoroethanol. The chitin binding property of the peptide was also confirmed by fast performance liquid chromatography.

Cloning and characterization of a novel 2-ketoisovalerate reductase from the beauvericin producer Fusarium proliferatum LF061

BackgroundThe ketoisovalerate reductase (EC 1.2.7.7 ) is required for the formation of beauvericin via the nonribosomal peptide synthetase biosynthetic pathway. It catalyzes the NADPH-specific reduction of ketoisovaleric acid to hydroxyisovalerate. However, little is known about the bioinformatics’ data about the 2-Kiv reductase in Fusarium. To date, heterologous production of the gene KivRFp from Fusarium has not been achieved.ResultsThe KivRFp gene was subcloned and expressed in Escherichia coli BL21 using the pET expression system. The gene KivRFp contained a 1,359 bp open reading frame (ORF) encoding a polypeptide of 452 amino acids with a molecular mass of 52 kDa. Sequence analysis indicated that it showed 61% and 52% amino acid identities to ketoisovalerate reductase from Beauveria bassiana ATCC 7159 (ACI30654) and Metarhizium acridum CQMa 102 (EFY89891), respectively; and several conserved regions were identified, including the putative nucleotide-binding signature site, GXGXXG, a catalytic triad (Glu405, Asn184, and Lys285). The KivRFp exhibited the highest activity at 35°C and pH 7.5 respectively, by reduction of ketoisovalerate. It also exhibited the high level of stability over wide temperature and pH spectra and in the presence of metal ions or detergents.ConclusionsA new ketoisovalerate reductase KivRFp was identified and characterized from the depsipeptide-producing fungus F. proliferatum. KivRFp has been shown to have useful properties, such as moderate thermal stability and broad pH optima, and may serve as the starting points for future protein engineering and directed evolution, towards the goal of developing efficient enzyme for downstream biotechnological applications.

Abstracts of the 17th International Symposium on Bioluminescence and Chemiluminescence ‐ (ISBC 2012)

WARNING : The light-emitting molecular structures responsible for the chemiluminescence and fluorescence phenomena are not necessarily the same!

Assessment of Substrate Inhibition of Bacterial Oligopeptidase B

Oligopeptidase B (OPB; EC 3.4.21.83) from 2 Gram-negative bacteria, Stenotrophomonas maltophilia (Stm) and Serratia marcescens (Sem), and the Gram-positive bacterium Rhodococcus erythropolis (Re) were cloned and characterized to clarify their activities and substrate specificities using peptidyl-MCA substrates containing Arg or Lys. The cloned enzymes, Stm, Sem and ReOPBs, in addition to Escherichia coli OPB (EcOPB) were expressed using a pET expression system. Although the Stm and SemOPBs share 45% sequence identity to each other and up to 60% identity with respect to their catalytic domains, their activities towards MCA substrates were quite different. StmOPB is approximately 100-500 times more active than SemOPB and 3-30 times more active than EcOPB. The activity of ReOPB is comparable to that of StmOPB and it shares 40% and 36% identity to StmOPB and SemOPB, respectively. Some features of Stm, Re and EcOPBs are similar to those of previously cloned OPBs, which were also strongly inhibited by substrates, but SemOPB differs from all other OPBs in that it is not inhibited by substrates; even substrates containing double arginine at 35 µM did not inhibit SemOPB. On the other hand, the same substrates at only 5 µM inhibited the activity of the Stm, Re, and EcOPB. This phenomenon was not observed with substrates containing single or double lysine.

Immunological Identification and Characterization of Extracellular Serine Protease-Like Protein Encoded in a Putative <i>espP2</i> Gene of <i>Haemophilus parasuis</i>

Haemophilus parasuis is known to produce a group of virulence-associated autotransporter (AT) proteins, VtaAs; however, no other ATs have been characterized yet. On the basis of the reported sequence of a putative espP2 gene for extracellular serine protease (ESP)-like protein of H. parasuis, this putative AT gene was successfully amplified from H. parasuis serotype 5 field strain HPS0819, cloned and sequenced. The confirmed ORF sequence showed 100% identity with the reported putative espP2 gene. The recombinant ESP-like protein purified from Escherichia coli with a pET expression system was used for immunological characterization. An approximately 85 kDa antigen was detected in cultured H. parasuis by using antiserum to the purified ESP-like protein, and antibodies against the recombinant ESP-like protein were detected in a selected serum from pigs with experimental H. parasuis infection. The results indicated that H. parasuis could produce ESP-like protein in vitro and in vivo. In an immune protection study using guinea pigs, 6 out of 10 animals immunized with the recombinant ESP-like protein survived after challenge with 5 × 10(9) bacteria of strain HPS0819, whereas 7 out of 10 animals immunized with formalin-inactivated H0819 bacterin survived after challenge. The results suggest that ESP-like protein could be one of the vaccine antigen candidates for H. parasuis infection.