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Clinical and Diagnostic Laboratory Immunology, December 2005, p. 1451-1454, Vol. 12, No. 12
1071-412X/05/$08.00+0 doi:10.1128/CDLI.12.12.1451-1454.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Immunoglobulin E Binding Reactivity of a Recombinant Allergen Homologous to
-Tubulin from Tyrophagus putrescentiae
Kyoung Yong Jeong,1
Haeseok Lee,1
Jae Sik Lee,1
Jongweon Lee,1
In-Yong Lee,1
Han-Il Ree,1
Chein-Soo Hong,2
Jung Won Park,2 and
Tai-Soon Yong1*
Department of Parasitology and Institute of Tropical Medicine,1
Department of Internal Medicine and Institute of Allergy, Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Korea2
Received 17 April 2005/
Returned for modification 11 July 2005/
Accepted 5 August 2005

ABSTRACT
Storage mites may cause allergic respiratory diseases in urban
areas as well as pose an occupational hazard in rural areas.
Characterization of storage mite allergens is important for
the development of diagnostic and therapeutic agents against
mite-associated allergic disorders. Here we report on the cloning
and expression of

-tubulin from the storage mite (
Tyrophagus putrescentiae). The deduced amino acid sequence of the

-tubulin
from the storage mite showed as much as 97.3% identity to the

-tubulin sequences from other organisms. The highly conserved
amino acid sequences of

-tubulins across different species of
mites may indicate that cross-reactivity for this potential
allergen exists. The frequency of immunoglobulin E reactivity
of this recombinant protein is 29.3% in sera from storage mite-allergic
subjects.

TEXT
It is known that sensitization to allergens derived from storage
mites may lead to occupational allergic disorders (
2,
3). There
has been increasing interest in the allergenicity of storage
mites in recent years (
13). In epidemiological studies, the
predominant species in Korean homes were found to be
Dermatophagoides farinae (65 to 77%) and
Dermatophagoides pteronyssinus (8 to
20%) (
7,
15).
Tyrophagus putrescentiae was reported to be the
third most common domestic mite, infesting 6.5 to 8.5% of Korean
homes (
7,
15). In a study with sera from atopic urban inhabitants,
a marked inhibition of
T. putrescentiae-specific immunoglobulin
E (IgE) by
D. farinae and
D. pteronyssinus extract was demonstrated,
while
D. pteronyssinus- or
D. farinae-specific IgE was partially
inhibited by a
T. putrescentiae extract (
14). Significant cross-reactivity
between other arthropods and nematodes was also reported (
9).
The prevalence of storage mite sensitization was reported in
a general adult population in Spain (
18), and the allergen-specific
IgE (CAP) correlation analysis in Spain also showed allergenic
similarity between
Dermatophagoides spp. and storage mites,
such as
T. putrescentiae,
Glycyphagus domesticus, and
Acarus siro (
10). Molecular cloning of Tyr p 2 and Tyr p 13 from
T. putrescentiae has been done (
5,
8). In addition, molecular modeling
has found many amino acid substitutions at surface residues
of Tyr p 2 that still conserve its tertiary structure (
17).
These substitutions may indicate that there is limited cross-reactivity
for group 2 allergens among different mite species. Moreover,
group 13 allergens have not been identified from
Dermatophagoides spp. Identification of more allergens and their characterization
in molecular detail will allow us to better understand the cross-reactivity
for mite species. In this respect, expressed sequence tag (EST)
strategies could be useful for the identification of cross-reactive
allergens present in house dust mite and storage mite (
1,
8).
We previously identified several candidate allergen molecules by analyzing an EST database of T. putrescentiae (8). Here we describe the expression of recombinant
-tubulin and its allergenic characterization.
An
-tubulin was first identified as a putative allergen from a phage display Lepidoglyphus destructor cDNA library (16). There are multiple
-tubulin genes in most organisms, and they are highly conserved within and among species (4, 11, 12).
A cDNA sequence encoding
-tubulin was obtained by analyzing T. putrescentiae EST clones. Both strands of the cDNA were sequenced. The insert cDNA was 1,604 bp in length and contained a single open reading frame of 1,364 bp which started at ATG (nucleotide [nt] 1) and which terminated at stop codon TAA (nt 1351) (Fig. 1). The estimated molecular mass was 50.04 kDa, and the calculated isoelectric point was 4.834. The deduced amino acid sequence of the T. putrescentiae
-tubulin showed as much as 97.3% identity to the
-tubulin sequences from other organisms (Fig. 2). A PROSITE search revealed a tubulin consensus sequence, [SAG]-G-G-T-G-[SA]-G (which is known to interact with GTP at positions 142 to 148), and one N-glycosylation site (positions 380 to 382) (6).
A PCR was carried out to introduce a BamHI site upstream of
the start codon and a HindIII site just downstream of the stop
codon. The following synthetic oligonucleotides were used as
primers:
GGATCCTATGCGCGAATGTATCTC (forward primer) and
AAGCTTCCACTTAGAATTCCTCTC
(reverse primer) (underlining indicates restriction sites).
The resulting PCR fragment was subcloned into the pGEM-T Easy
vector (Promega, Madison, WI) and was then digested with BamHI
plus HindIII. The DNA fragment was subsequently ligated into
the pET 28b vector. When this construct was used, 34 additional
amino acids are added at the N terminus of the

-tubulin. The
bacterial transformant was induced to express the recombinant
protein by the addition of 1 mM isopropyl-1-thio-ß-galactopyranoside
after the cells had grown to an
A600 of 0.6. After sonication,
a 56-kDa protein was detected by sodium dodecyl sulfate-polyacrylamide
gel electrophoresis in the total cell lysate and in the insoluble
precipitate. The protein was solubilized in 20 mM Tris, 500
mM NaCl, 5 mM imidazole, and 6 M urea, pH 7.9. It was then purified
by using nickel-nitrilotriacetic acid resin (QIAGEN, Valencia,
CA) (Fig.
3). The purified protein was desalted and concentrated
with a Centriprep filter (YM-10; Millipore, Bedford, MA). The
yield of purified recombinant protein was 4.576 mg/liter of
bacterial culture.
To test the IgE reactivity of the recombinant protein, an enzyme-linked
immunosorbent assay (ELISA) was performed with sera from
T. putrescentiae-sensitized subjects diluted 1:4. Sera were obtained
from allergic patients attending the Allergy Clinic of the Severance
Hospital, Yonsei University, Seoul, Korea; and the diagnosis
was based on the patient's case history and the results of a
skin prick test (Allergopharma, Reinbek, Germay). All the subjects
were tested for the presence of IgE antibodies against
T. putrescentiae by using the Uni-CAP system (Pharmacia, Uppsala, Sweden). Those
sera with allergen-specific IgE levels (CAP results) between
and 17.5 kU/liter were used for the ELISA (
n = 41 patients;
age range, 7 to 69 years; average age, 32 years). The results
of the ELISA with
T. putrescentiae crude extract showed a good
correlation (
r2 = 0.81) with the specific IgE levels investigated
by use of the Uni-CAP system. The nonatopic sera from 20 subjects
who were not sensitized to the 50 allergens tested were used
as negative controls. Informed consent was obtained from the
subjects before the experiments with the sera were performed.
The optimal condition of the antigen and the antibody concentration
were determined by checkerboard titrations. Purified

-tubulin
(2.0 µg/ml) in coating buffer (0.1 M sodium carbonate,
pH 9.6) was coated onto the microtiter plate (0.1 ml/well),
and the plate was incubated overnight at 4°C. The plate
was then incubated with human sera for 1 h after it was blocked
with 3% skim milk. Antibodies that bound to recombinant

-tubulin
were detected by using biotinylated goat anti-human IgE (1:1,000)
(Vector, Burlingame, CA) and streptavidin-peroxidase (1:1,000;
Sigma, St. Louis, MO). The microtiter plate was washed with
phosphate-buffered saline containing 0.05% Tween 20 between
each step before color development. The signals were developed
by using 3,3',5,5'-tetramethylbenzidine (Kirkegaard & Perry
Laboratories, Gaithersburg, MD) as the substrate, and the optical
density was determined at 450 nm by using an automatic microplate
reader (TECAN, Salzburg, Austria). The ELISA showed a frequency
of IgE binding to recombinant

-tubulin of 29.3% (12 of 41 samples)
when the mean absorbance level for the serum samples from the
20 controls plus 2 standard deviations was used as the cutoff
value (
P = 0.08) (Fig.
4).
The IgE reactivity may be influenced by a difference between
recombinant and native protein folding or the lack of glycosylation,
since no posttranslational modifications occur in the
Escherichia coli expression system. The recombinant

-tubulin derived from
Lepidoglyphus destructor showed an 11.6% (11 of 95 samples)
IgE-binding frequency (
16). Inhibition studies for evaluation
of the allergenic potency could not be performed due to its
low concentration in the whole-body extract.
Here we elucidated the primary structure of
-tubulin, an important potential allergen, from T. putrescentiae and expressed the recombinant protein. The clinical relevance of this allergen remains to be evaluated in vivo. The highly conserved amino acid sequences of
-tubulins among different species may indicate that cross-reactivity for this protein exists. To investigate this possible cross-reactivity, molecular cloning of
-tubulins from house dust mites such as D. farinae and D. pteronyssinus, which are known to be major sources of mite allergens, is needed. The
-tubulin cloned in this study will facilitate examination of the involvement of this class of allergens in the development of mite-associated allergic diseases. It is also hoped that the use of recombinant
-tubulin in combination with other allergens may improve the diagnostic specificity.
Nucleotide sequence accession number.
The nucleotide sequence reported in this paper has been deposited in the GenBank sequence database under accession number AY986760.

ACKNOWLEDGMENTS
This study was supported by the Brain Korea 21 Project for Medical
Science, Yonsei University.

FOOTNOTES
* Corresponding author. Mailing address: Department of Parasitology and Institute of Tropical Medicine, Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul 120-752, Korea. Phone: 82-2-228-1840. Fax: 82-2-363-8676. E-mail:
tsyong212{at}yumc.yonsei.ac.kr.


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Clinical and Diagnostic Laboratory Immunology, December 2005, p. 1451-1454, Vol. 12, No. 12
1071-412X/05/$08.00+0 doi:10.1128/CDLI.12.12.1451-1454.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.