[Cloning, expression and identification of Der f7 gene from Dermatophagoides farinae and its immunological characteristics]

OBJECTIVE

To clone and express Der f7 gene of Dermatophagoides farinae, and identify its immunogenicity.

METHODS

Total RNA was extracted from D. farinae mites. A reference sequence (Accession No. AY283292) was used to design specific primers. The Der f7 gene fragment was amplified by RT-PCR, and cloned into pET-32a vector. The recombinant plasmid was transformed into E. coli BL21 (DE3) and induced with IPTG for protein expression. The recombinant protein was purified by Ni2+ chelating affinity chromatography and analyzed by SDS-PAGE and Western blotting.

RESULTS

The Der f7 gene fragment was about 650 bp, and shared 99% homology with the published one (Accession No. FJ436108). SDS-PAGE result showed its relative molecular weight (M(r)) of 23 000. The recombinant protein showed appropriate combination ability with IgE in sera of mite allergic patients.

CONCLUSION

Der f 7 gene has been expressed in prokaryotic expression system and shows allergenicity.

The proline-rich motif of the proDer p 3 allergen propeptide is crucial for protease-protease interaction

The majority of proteases are synthesized in an inactive form, termed zymogen, which consists of a propeptide and a protease domain. The propeptide is commonly involved in the correct folding and specific inhibition of the enzyme. The propeptide of the house dust mite allergen Der p 3, NPILPASPNAT, contains a proline-rich motif (PRM), which is unusual for a trypsin-like protease. By truncating the propeptide or replacing one or all of the prolines in the non-glycosylated zymogen with alanine(s), we demonstrated that the full-length propeptide is not required for correct folding and thermal stability and that the PRM is important for the resistance of proDer p 3 to undesired proteolysis when the protein is expressed in Pichia pastoris. Additionally, we followed the maturation time course of proDer p 3 by coupling a quenched-flow assay to mass spectrometry analysis. This approach allowed to monitor the evolution of the different species and to determine the steady-state kinetic parameters for activation of the zymogen by the major allergen Der p 1. This experiment demonstrated that prolines 5 and 8 are crucial for proDer p 3-Der p 1 interaction and for activation of the zymogen.

Epitope mapping and in silico characterization of interactions between Der p 7 allergen and MoAb WH9

Der p 7 is an important house dust mite allergen. However, antigenic determinants of Der p 7 are largely unknown. The purpose of this study is to analyze the determinants of Der p 7 and determine the structural basis of interactions between Der p 7 and WH9, an IgE-binding inhibition mouse monoclonal antibody (MoAb). IgE and WH9-reactive determinant(s) was identified by immunoblot using allergen mutants. A 3-D binary complex structure of Der p 7 and WH9 was simulated with homology modeling and docking methods. Our results obtained showed that among the five Der p 7 mutants (S156A, I157A, L158A, D159A, P160A), serum no. 1045 with IgE-binding against Der p 7 exhibited a reduced IgE immunoblot reactivity against Der p 7 L158A and D159A mutants. WH9 showed reduced immunoblot reactivity against S156A, L158A, D159A and P160A and the observation was confirmed by immunoblot inhibition. The WH9-binding determinant on Der p 7 containing S156, L158, D159 and P160 assumes a loop-like structure. The structural model of the Der p 7-WH9 complex suggests residues S156, I157, L158, D159 and P160 of Der p 7 contribute to WH9 binding via potential hydrogen bonds, electrostatic and hydrophobic interactions. In conclusion, MoAb WH9 interacts with critical residues L158 and D159 of Der p 7 and inhibits IgE-binding to Der p 7. Results obtained advance our understanding on molecular and structural bases of the antigenicity of Der p 7, its interactions with MoAb WH9 and facilitate the design of safer immunotherapy of human atopic disorders.

Production of a chimeric allergen derived from the major allergen group 1 of house dust mite species in Nicotiana benthamiana

Plants are widely accepted as a general platform for the large-scale production of recombinant proteins, which has been demonstrated by the successful expression of various exogenous proteins. Using plants as a bioreactor for mass production of target proteins for vaccines is thought to show the most potential. This study explores whether a chimeric allergen R8, derived from the major allergen group 1 of house dust mites species (Dermatophagoides farinae and Dermatophagoides pteronyssinus), is expressed in tobacco. The highly efficient and useful Tobacco mosaic virus RNA-based overexpression (TRBO) vector was used to investigate expression of the R8 molecule in tobacco by agroinfection. Presence of R8 was detected using SDS-PAGE and Western blotting. Purified allergens were characterized using IgE-binding activity assay and allergen-specific immunotherapy (ASIT) in murine asthmatic models. The recombinant R8 was successfully expressed in tobacco leaves. The pro-peptide was observed in the herbaceous leaf extracts. This protein exhibits properties similar to the parental allergen ProDer f 1 expressed in Escherichia coli or tobacco with respect to IgE immunoreactivity. R8 also rectifies imbalance of TH1/TH2 cells. An herbaceous plant expression system model allows mass production of R8, which might be used in the future for diagnosis of asthma or production of a candidate vaccine for allergen-specific immunotherapy of asthma.

The group 10 allergen of Dermatophagoides farinae (Acari: Pyroglyphidae): cDNA cloning, sequence analysis, and expression in Escherichia coli BL21

Dermatophagoides farinae Hughes, American house dust mite, is highly allergenic, producing symptoms in people worldwide. Identifying and cloning the allergens in this species may enable better diagnostic and therapeutic approaches. Here, we cloned, sequenced, and expressed the full-length cDNA encoding D. farinae group 10 allergen (Der f 10) isolated from dust mites in China. Bioinformatic analysis indicated that the 888 bp sequence encoded a cytoskeleton protein 295 amino acids long, with a molecular weight of approximately equal 34 kDa. Sequence alignment with the group 10 allergens of Pyroglyphidae, Acaridae, and Glycyphagidae families revealed that the group 10 allergen from D. farinae is 95% similar to D. pteronyssinus Trouessart and Psoroptes ovis (Hering). These findings lay the groundwork for future studies, including large-scale production of recombinant Der f 10 allergen for diagnostic and therapeutic agents.

Sequence polymorphisms of Der f 1, Der p 1, Der f 2 and Der p 2 from Korean house dust mite isolates

Amino acid sequence variations have possible influences on the allergenicity of allergens and may be important factors in allergen standardization. This study was undertaken to investigate the sequence polymorphisms of group 1 and 2 allergens from Korean isolates of the house dust mites Dermatophagoides farinae and D. pteronyssinus. cDNA sequences encoding group 1 and 2 allergens were amplified by RT-PCR and compared the deduced amino acid sequences. Der f 1.0101, which appeared in 64.0 % of the 50 sequences analyzed, was found to be predominant. Among the Der p 1 sequences, Der p 1.0102 and 1.0105 were predominant (58 %). Among the Der f 2 sequences, Der f 2.0102 (40.7 %) and a new variant with Gly at position 42 (27.8 %) were predominant. The deduced amino acid sequences of 60 Der p 2 clones were examined, and 28 variants with 1-5 amino acid substitutions were found. Interestingly, all of the Der p 2 sequences had Thr instead of Lys at position 49. Two variants (Leu40, Thr49, and Asn114 (26.6 %); Val40, Thr49, and Asn114 (20.0 %)) were found to be the most predominant forms of Der p 2. Der p 1 has a high rate of sporadic substitutions and the group 2 allergens show a more regular pattern with orderly associations of amino acid substitutions. Der f 1 and Der p 2 from Korean mite isolates have unique amino acid sequence polymorphisms. These findings provide important data for house dust mite allergen standardization.

In planta expression of a mature Der p 1 allergen isolated from an Italian strain of Dermatophagoides pteronyssinus

European (Dermatophagoides pteronyssinus) and American (Dermatophagoides farinae) house dust mite species are considered the most common causes of asthma and allergic symptoms worldwide. Der p 1 protein, one of the main allergens of D. pteronyssinus, is found in high concentration in mites faecal pellets, which can became easily airborne and, when inhaled, can cause perennial rhinitis and bronchial asthma. Here we report the isolation of the Der p 1 gene from an Italian strain of D. pteronyssinus and the PVX-mediated expression of its mature form (I-rDer p 1) in Nicotiana benthamiana plants. Human sera from characterized allergic patients were used for IgE binding inhibition assays to test the immunological reactivity of I-rDer p 1 produced in N. benthamiana plants. The binding properties of in planta produced I-rDer p 1 versus the IgE of patients sera were comparable to those obtained on Der p 1 preparation immobilized on a microarray. In this paper we provide a proof of concept for the production of an immunologically active form of Der p 1 using a plant viral vector. These results pave the way for the development of diagnostic allergy tests based on in planta produced allergens.

Cloning, expression, purification, crystallization and preliminary X-ray diffraction studies of a major group 7 allergen, Der f 7, from the dust mite Dermatophagoides farinae

Der f 7 is a major group 7 allergen from the dust mite Dermatophagoides farinae that shows 86% sequence identity to the homologous allergen Der p 7 from D. pteronyssinus. Der f 7 was successfully overexpressed in an Escherichia coli expression system and purified to homogeneity using Ni-NTA affinity and size-exclusion column chromatography. SeMet-labelled Der f 7 was crystallized by the hanging-drop vapour-diffusion method using a reservoir solution consisting of 0.1 M bis-tris pH 7.4 and 28% polyethylene glycol monomethyl ether 2000 at 293 K. X-ray diffraction data were collected to 2.24 Å resolution using synchrotron radiation. The crystals belonged to the orthorhombic system, space group P2(1)2(1)2(1), with unit-cell parameters a = 50.19, b = 58.67, c = 123.81 Å. Based on the estimated Matthews coefficient (2.16 Å(3) Da(-1)), two molecules of Der f 7 could be present in the asymmetric unit of the crystal lattice.

Prevention of allergic asthma by vaccination with transgenic rice seed expressing mite allergen: induction of allergen-specific oral tolerance without bystander suppression

This study tested the feasibility of oral immunotherapy for bronchial asthma using a newly developed subunit vaccine in which a fragment (p45-145) of mite allergen (Der p 1) containing immunodominant human and mouse T cell epitopes was encapsulated in endoplasmic reticulum-derived protein bodies of transgenic (Tg) rice seed. Allergen-specific serum immunoglobulin responses, T cell proliferation, Th1/Th2 cytokine production, airway inflammatory cell infiltration, bronchial hyper-responsiveness (BHR) and lung histology were investigated in allergen-immunized and -challenged mice. Prophylactic oral vaccination with the Tg rice seeds clearly reduced the serum levels of allergen-specific IgE and IgG. Allergen-induced CD4(+) T cell proliferation and production of Th2 cytokines in vitro, infiltration of eosinophils, neutrophils and mononuclear cells into the airways and BHR were also inhibited by oral vaccination. The effects of the vaccine were antigen-specific immune response because the levels of specific IgE and IgG in mice immunized with Der f 2 or ovalbumin were not significantly suppressed by oral vaccination with the Der p 1 expressing Tg rice. Thus, the vaccine does not induce nonspecific bystander suppression, which has been a problem with many oral tolerance regimens. These results suggest that our novel vaccine strategy is a promising approach for allergen-specific oral immunotherapy against allergic diseases including bronchial asthma.

Mite allergens: an overview

Mite allergens from the Pyroglyphidae family are the most frequent and potent sources of perennial asthma and rhinitis. Since 1988 molecular knowledge has considerably increased and structures and functions have been determined for most of them. Of the 22 denominated allergens, Der p 1 and Der p 2 are major allergens recognized by more than 80% of lgE from Dpt allergic patients in Europe. Der p 4, Der p 5 and Der p 7 appeared to be intermediate allergens. The binding of IgE to groups 3, 6, 8, 9, 10 and 20 is constantly low. Most of the allergens can be identified by amino-acid sequences and the tertiary structure of the major allergens has been solved. Most Dpt mite allergens are proteolytic enzymes: Der p 1 for instance is a cysteine protease. Der p 2 has structural homology with MD-2, a co-receptor of the Toll-like receptor (TLR4) whose ligand is LPS. Knowledge of the mite allergens structure has allowed a better interpretation of cross reactions between allergens from the same family or from more distant families. From a practical point of view molecular epidemiology has allowed a better choice of allergen molecules useful for diagnosis. Finally, new concepts of immunotherapy based on genetically engineered hypoallergenic variants of major allergens, used alone or in combination, can be considered.

Asp159 is a critical core amino acid of an IgE-binding and cross-reactive epitope of a dust mite allergen Der f 7

Der f 7 and Der p 7 are important house dust mite allergens with known structure and suggested biological function recently. However, their IgE-binding determinants remain unknown. The purpose of this study is to identify the IgE-reactive epitopes of Der f 7 and the determinants of IgE-mediated cross-reactivity between Der f 7 and Der p 7. IgE-reactive determinants were identified by immunodot blot inhibition using synthetic overlapping peptides, allergen mutants, and a Der f 7 structural model. Our results showed that synthetic peptides with sequence (156)SILDP(160) on Der f 7 bind IgE in two of the 30 asthmatic serum samples tested. Recombinant Der f 7 I157A, L158A, or D159A mutants have reduced IgE-binding activity. Inhibition experiments confirmed Asp159 as a critical core residue for IgE-binding. Among Der p 7, Der f 7 and Der f 7 mutants with single substitution between residues 156 and 160, only the D159A mutant cannot inhibit significantly IgE-binding against Der p 7. Therefore, Asp159 contributes to IgE-mediated cross-reactivity between Der f 7 and Der p 7. The structural model constructed for Der f 7 suggests that the IgE-binding epitope forms a loop-like structure on the surface of the molecule. In conclusion, Asp 159 is a critical core residue of an IgE-binding and IgE-mediated cross-reactive epitope (156)SILDP(160) of Der f 7. Results obtained from this study provide more information on molecular and structural features related to allergenicity, underlying basis of IgE cross-reactivity between allergens, and in designing safer immunotherapy.

Derp2-mutant gene vaccine inhibits airway inflammation and up-regulates Toll-like receptor 9 in an allergic asthmatic mouse model

BACKGROUND

A DNA vaccine encoding the whole segment of the Derp2 allergen could prevent allergic airway inflammation in a Derp2 allergen-induced allergic airway inflammation mouse model.

OBJECTIVE

This study investigated the effect of DNA vaccine encoding Derp2-mutant gene in which an IgE epitope was deleted on airway inflammation and the role of TLR9 in the asthmatic mouse model.

METHODS

A Derp2-mutant DNA vaccine was constructed. Mice were immunized, sensitized and challenged. Airway inflammation, airway hyper reactivity (AHR) and serum antibody were tested. The expression of Toll like receptor9 (TLR9) was detected with western-blot and immunehistochemistry.

RESULTS

We demonstrated that the Derp2-mutant-DNA induced IgG2a and inhibited IgE production, inhibited airway allergenic inflammation and AHR. Derp2-mutant-DNA vaccine induce TLR9 expression in lung tissue.

CONCLUSIONS

The data indicate that allergen DNA vaccine deleted IgE epitope could prevent allergenic airway inflammation, AHR, and upregulate lung TLR9 express.

Geography of house dust mite allergens

OBJECTIVE

To consider how the different distribution of house dust mites and their species in different geographical locations affects the allergens in the environment and their use.

DATA SOURCES

Data were obtained from Medline, Genbank and library and web searches.

STUDY SELECTIONS

A comprehensive description of the genetic variations of allergens is given. The distribution of house dust mites is illustrated with publications that either make pertinent observations or would be useful for a broad appreciation of their geographical distribution.

RESULTS

The review identifies regions where glycyphagid house dust mites have been found and the distribution of the pyroglyphid Dermatophagoides spp. The antigenic differences the allergens of D. pteronyssinus and D. farinae are outlined and how this should affect optimal allergen usage in different regions. The allelic variations within the major allergens of Dermatophagoides sp. are similarly presented.

CONCLUSIONS

While there is a broad knowledge of the distribution of different species of house dust mites, regions that require further examination have been identified and there are examples of incorrect use of allergens for different regions. The extension of allergy research and practice into new regions will benefit from allergen formulations designed for regional use. Specific knowledge of the allergens in the environments will be required to optimally implement some of the new molecularly-defined medicaments currently being developed for effective allergy vaccination and immunotherapy.

Cloning, expression, and characterization of Der f 7, an allergen of Dermatophagoides farinae from China

A full-length cDNA encoding house dust mite allergen Der f 7 from Dermatophagoides farina (Acari: Pyroglyphidae) from China was cloned, sequenced, and successfully expressed. A reference sequence (GenBank accession AY283292) was used to design polymerase chain reaction primers. Analysis revealed eight mismatched nucleotides in five Der f 7 cDNA clones, and the projected amino acid sequence contained six incompatible residues. These results suggest that the sequence of Der f 7 may be polymorphic. Further bioinformatic analysis revealed that the mature Der f 7 allergen had a molecular mass of approximately 21.88 kDa and a theoretical isoelectric point of 4.90. Der f 7 protein secondary structure was composed of a helix (56.63%), extended strand (5.10%), and random coil (38.27%). Group 7 allergens are present in Pyroglyphidae, Acaridae, and Glycyphagidae families, and homology analysis revealed a 86% similarity between Der f 7 and Der p 7. Furthermore, a phylogenetic tree constructed of group 7 allergens from different mite species revealed that Der f 7 and Der p 7 clustered with 100% bootstrap support. Bioinformatics-driven characterization of Der f 7 allergen as conducted in this study may contribute to diagnostic and therapeutic applications for dust mite allergies.

Analysis of expression and amino acid sequence of the allergen Mag 3 in two species of house dust mites-Dermatophagoides farinae and D. pteronyssinus (Acari: Astigmata: Pyroglyphidae)

In the 90's of the XX century, 2 new and important allergens of house dust mites mites were cloned and sequenced: Mag 1 and Mag 3. However, the second allergen has been identified to date only in extracts of Dermatophagoides farinae [DF ]. In this work, we aimed to detect expression of this important allergen and for the first time analyze to the amino acid sequence in other species of house dust mite - Dermatophagoides pteronyssinus [DP ]. We were able to confirm the expression of allergen Mag 3 in DF and to exclude it in DP . By sequencing the products of DNA amplification, we revealed the nucleotide sequence encoding allergen Mag 3 in DF . This analysis enabled detection of 9 single base changes. An analysis of encoded amino acid sequence by triplets with substituted nucleotides revealed that 8 changes were polymorphic, and 1 was a mutation substituting GTG (valine) for ATG (methionine) at 236 position. However, the presence of amino acid sequence difference in this allergen might suggest that there exist other isoforms which can make difficult both diagnosis as well as immunotherapy in persons who produce allergic response to this allergen. The variants of allergen Mag 3 (group 14) are still not known beside the very good known allergen variants of the other main groups 1, 2, 4, 5 or 7. Thus, the identification and definition of allergic properties of allergen Mag 3 variants needs to be further investigated.

Production and immunogenicity of hypoallergenic codon-optimized DNA vaccine encoding mature Der p 1 allergen

BACKGROUND

Genetic vaccination with plasmid DNA encoding allergens is a promising potential approach for the treatment or prevention of allergy. Nonetheless, because the allergens expressed can display immunoglobulin (Ig) E reactivity, methods to deliver hypoallergenic variants can minimize the risk of type 2 helper (T(H)2) cell priming after DNA immunization.

METHODS

A humanized synthetic gene encoding mature Dermatophagoides pteronyssinus group 1 (Der p 1) allergen was cloned into the pHIS expression vector carrying unmethylated CpG 2006 (CpG 2006) motif but devoid of signal sequence. The immunogenicity of this DNA construct was compared in naïve mice with that of recombinant ProDer p 1 protein adjuvanted with alum.

RESULTS

Codon optimization of the cDNA encoding mature Der p 1 markedly improved allergen expression. Mature Der p 1, expressed intracellularly in Human Embryonic Kidney 293 cells (HEK 293 cells) transfected with codon-optimized Der p 1 cDNA (pHIS-mHuDer p 1), was shown to be hypoallergenic as it displayed no IgE reactivity. Intradermal vaccinations of naïve Balb/C mice with pHIS-mHuDer p 1 elicited an allergen-specific T(H)1 response characterized by the production of specific IgG2a, a very low amount of specific IgG1, and no specific IgE. Lipoplex formulation with cationic liposome composed of lecithin, N-[1-(2,3-Dioleoyloxy)propyl]-N,N,N-trimethylammonium methylsulfate (DOTAP) and cholesterol not only accelerated the induction of T(H)1 response but also increased its intensity.

CONCLUSION

A codon-optimized DNA vaccine encoding mature Der p 1 in a lipoplex formulation could represent a promising hypoallergenic vaccine candidate for safer immunotherapy against house dust mite allergy.

Cloning, sequence analysis and expression in E. coli of the group 3 allergen of Dermatophagoides farinae

BACKGROUND

The dust mites, which are mostly represented by Dermatophagoides spp. (Acari: Pyroglyphidae), are the major sources of indoor allergens. Identification and characterization of these mite allergen molecules are an important step in the development of new effective diagnostic procedures and possible therapeutic strategies for allergic disorders associated with dust mites.

METHODS

Total RNA was extracted from Dermatophagoides farinae. The gene coding for Der f 3 was amplified by RT-PCR with the primers designed based on previous sequence published in GenBank. The target gene was cloned intermediately into pMD19-T plasmid and finally into plasmid pET28a (+), expressed in E. coli BL21 at the aid of the inducer isopropyl-D-thiogalactopyranoside (IPTG). The physicochemical properties, spatial structure of the allergen were analyzed with bioinformatics software.

RESULTS

The cDNA coding for group 3 allergen of Dermatophagoides farinae from China was cloned and expressed successfully. Sequencing analysis showed that there were nineteen mismatched nucleotides in five Der f 3 cDNA clones in comparison with the reference (GenBank Accession No. AY283291), which resulted in deduced amino acid sequence incompatibility in eleven residues. Bioinformatics analysis revealed that the Der f 3 pro-protein was an extracellular hydrophobic protein, consisting of 259 amino acids with a 16 amino acid signal peptide. The protein was deduced to have three chymotrypsin active sites (53-68 AA, 108-122 AA and 205-217 AA), one N-glycosylation site, one cAMP- and cGMP-dependent protein kinase phosphorylation site, four protein kinase C phosphorylation sites, two casein kinase II phosphorylation sites, and five N-myristoylation sites.

CONCLUSIONS

Der f 3 is an extracellular hydrophobic protein which possesses multiple activation and phosphorylation sites. Polymorphism may exist in the Der f 3 gene but this needs to be further confirmed in the future.

Enzyme-linked immunosorbent assays with high sensitivity for antigen-specific and total murine IgE: a useful tool for the study of allergies in mouse models

BACKGROUND

In studies on allergies in mouse models, IgE production is an essential parameter to be evaluated. Here, we examine the effect of commercially available immunoreaction enhancer solutions and different blocking reagents in enzyme-linked immunosorbent assay (ELISA) for total or antigen-specific murine IgE in order to improve the assays.

METHODS

Sera from mice immunized with recombinant house dust mite major allergens, Der f 1 and Der p 1, were used for the assays. Total IgE was measured by sandwich ELISA using monoclonal antibodies against murine IgE. Antigen-specific IgE was assayed using allergen-coated plates. Sensitivity or signal intensity in ELISA was compared among conditions differing in the use of enhancer solutions, blocking reagents, or monoclonal antibodies, and incubation time.

RESULTS

Use of enhancer solutions improved the sensitivity of ELISA for total IgE by approximately 30-fold of that using a conventional buffer. A blocking reagent caused more unwanted enhancement of the background signal in blank wells in ELISA for total IgE compared with another blocking reagent, however, improved signal intensity in ELISA for antigen-specific ELISA without significant enhancement of the background signal. Optimal assay conditions were determined.

CONCLUSIONS

Enhancer solutions are effective in improving ELISAs for total and antigen-specific murine IgE. Selection of blocking reagents was important to decrease unwanted enhancement of background signals and was effective in enhancing signals for positive samples. The ELISAs improved in this study are useful for the study of allergies in mouse models.

Production of native and modified recombinant Der p 1 molecules in tobacco plants

BACKGROUND

As a complex molecule requiring post-translational processing, it has been difficult to produce the Der p 1 major allergen from the Dermatophagoides pteronyssinus house dust mite in a recombinant form.

OBJECTIVE

Here, we tested whether transgenic tobacco plants are suitable to express Der p 1, either as a wild-type molecule or as variants lacking N-glycosylation sites (Gly(-)) and/or cysteine protease activity (Enz(-)). Methods Using Agrobacterium tumefaciens-based transformation, pro Der p 1 molecules bearing mutations within either the N-glycosylation sites (N34Q, N150Q) and/or the cysteine protease-active site (C132V) were expressed in tobacco plants. After purification by ion exchange chromatography, allergens were characterized using immunoblotting, circular dichroism (CD), as well as basophil and T lymphocyte stimulation assays.

RESULTS

Four forms of recombinant Der p 1 (i.e. wild-type Gly(+)/Enz(+), as well as Gly(-)/Enz(+), Gly(+)/Enz(-) or Gly(-)/Enz(-) variants) were successfully expressed in tobacco leaves as pro Der p 1 molecules. Spontaneous cleavage of the pro-peptide was observed in tobacco leaf extracts for all forms of recombinant Der p 1 (r Der p 1). CD confirmed that all r Der p 1 molecules, with the exception of the Gly(-)/Enz(-) variant, exhibited secondary structures comparable to the natural protein. A cysteine protease activity was associated only with the Gly(+)/Enz(+) form. All these molecules exhibit a profile similar to natural Der p 1 with respect to IgE immunoreactivity, basophil activation and T cell recognition.

CONCLUSION

A tobacco plant expression system allows the production of various forms of mature Der p 1, which could be used for diagnostic or immunotherapeutic purposes.

Activation mechanism of recombinant Der p 3 allergen zymogen: contribution of cysteine protease Der p 1 and effect of propeptide glycosylation

The trypsin-like protease Der p 3, a major allergen of the house dust mite Dermatophagoides pteronyssinus, is synthesized as a zymogen, termed proDer p 3. No recombinant source of Der p 3 has been described yet, and the zymogen maturation mechanism remains to be elucidated. The Der p 3 zymogen was produced in Pichia pastoris. We demonstrated that the recombinant zymogen is glycosylated at the level of its propeptide. We showed that the activation mechanism of proDer p 3 is intermolecular and is mediated by the house dust mite cysteine protease Der p 1. The primary structure of the proDer p 3 propeptide is associated with a unique zymogen activation mechanism, which is different from those described for the trypsin-like family and relies on the house dust mite papain-like protease Der p 1. This is the first report of a recombinant source of Der p 3, with the same enzymatic activity as the natural enzyme and trypsin. Glycosylation of the propeptide was found to decrease the rate of maturation. Finally, we showed that recombinant Der p 3 is inhibited by the free modified prosequence T(P1)R.

Characterization of Der p 21, a new important allergen derived from the gut of house dust mites

BACKGROUND

The house dust mite (HDM) Dermatophagoides pteronyssinus is a major allergen source eliciting allergic asthma. The aim of the study was to identify new important HDM allergens associated with allergic asthma.

METHODS

A cDNA coding for a new mite allergen, designated Der p 21, was isolated using immunoglobulin E (IgE) antibodies from patients with allergic asthma out of a D. pteronyssinus expression cDNA library and expressed in Escherichia coli.

RESULTS

Circular dichroism analysis of the purified allergen showed that rDer p 21 (14 726 Da) is one of the few mite allergens with an alpha-helical secondary structure. The protein exhibited high thermal stability and refolding capacity, and, as determined by small angle X-ray scattering, formed a dimer consisting of two flat triangles. rDer p 21 bound high levels of patients' IgE antibodies and showed high allergenic activity in basophil activation experiments. Rabbit anti-Der p 21 IgG antibodies inhibited mite-allergic patients' IgE binding and allowed the ultrastructural localization of the allergen in the midgut (epithelium, lumen and faeces) of D. pteronyssinus by immunogold electron microscopy. Der p 21 revealed sequence homology with group 5 mite allergens, but IgE and IgG reactivity data and cross-inhibition studies identified it as a new mite allergen.

CONCLUSIONS

Der p 21 is a new important mite allergen which is liberated into the environment via faecal particles and hence may be associated with allergic asthma.

Bioinformatic studies on the group 2 allergens of Dermatophagoides farinae from China

The present study aimed to characterize the group 2 allergens of the house dust mite Dermatophagoides farinae (Der f 2) from Hainan Island, a tropical region in Southeastern China. We cloned and sequenced cDNA coding for Der f 2 and found an additional region of 87 base pairs (bp) (from +77 to +163 bp) in our strain that was absent in the reference sequence (GenBank AB195580) used for primer design. However, the BLAST analysis identified the same sequence in strains reported from Reinbek, Germany, and Guangzhou, China. A phylogenetic tree was constructed using the Der f 2 nucleotide sequences from different regions or countries and showed that the Hainan sequence clustered with the strains from Reinbek and Guangzhou. Analysis of the translated amino acid sequence suggests that the encoded peptide is hydrophobic and extracellular with a cleavage site between the 17th and 18th amino acid residues and contains a strong trans-membrane helix from the 6th amino acid to the 24th amino acid, indicating a MD-2-related lipid recognition domain in this protein. Furthermore, the secondary structure of the pro-protein consists of 16.57% alpha helix, 32.57% extended strand and 50.86% random coil. In brief, we obtained a gene coding for Der f 2 and predicted the molecular characteristics of this protein using bioinformatics tools. Our analysis identified that this gene showed several significant differences to those reported previously.