Characterization of api g 1.0201, a new member of the Api g 1 family of celery allergens.
BACKGROUND
The association of pollinosis with allergy to plant foods occurs in up to 70% of tree pollen-allergic patients. In recent years, some of the relevant cross-reacting proteins have been characterized at the molecular and immunological level. Api g 1 has been identified as the celery homologue of the major birch pollen allergen, Bet v 1. Although a number of Bet v 1 isoforms have been characterized from birch pollen, little is known about isoforms of food allergens and their allergenic features.


METHODS
Api g 1.0201, an isoform of Api g 1, was isolated from a cDNA library, cloned and sequenced. The cDNA was expressed in Escherichia coli and the purified recombinant protein was tested in immunoblots.


RESULTS
Api g 1.0201 displays 72% sequence similarity to the previously identified Api g 1.0101 and consists of 159 amino acid residues. The sequence of Api g 1.0201 has five additional amino acid residues at the carboxy-terminus as compared to Api g 1.0101. Purified recombinant Api g 1.0201 is recognized by IgE from the sera of celery-allergic patients, as well as by the murine monoclonal anti-Bet v 1 antibody. In general, this isoform displays a weaker IgE-binding capacity than Api g 1.0101, as concluded from immunoblotting experiments. Results from inhibition assays revealed that IgE-binding to Api g 1.0201 is only slightly reduced by preincubation with either purified recombinant Api g 1.0101 or purified recombinant Bet v 1a. Total inhibition was only achieved when using purified natural Bet v 1.


CONCLUSIONS
At present, little is known about the IgE-binding capacity of isoforms of Bet v 1 homologues of food allergens. Identification and characterization of such isoforms may help to contribute to a better understanding of food allergy and the observed cross-reactivity to pollen allergy.
Hoffmann-Sommergruber
K
K
Department of Pathophysiology, University of Vienna, Vienna, Austria. Karin.Hoffmann@akh-wien.ac.at
Ferris
R
R
Pec
M
M
Radauer
C
C
O'Riordain
G
G
Laimer Da Camara Machado
M
M
Scheiner
O
O
Breiteneder
H
H
D000485:Allergens / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology; D052179:Antigens, Plant; D019661:Apiaceae / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000032:analysis / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005512:Food Hypersensitivity / Q000097:blood / Q000276:immunology; D006801:Humans; D015151:Immunoblotting; D007073:Immunoglobulin E / Q000276:immunology / Q000378:metabolism; D007074:Immunoglobulin G / Q000276:immunology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D020033:Protein Isoforms; D017386:Sequence Homology, Amino Acid
D000485:Allergens; D000911:Antibodies, Monoclonal; D052179:Antigens, Plant; C096695:Api g 1 protein, Apium graveolens; D018076:DNA, Complementary; D007074:Immunoglobulin G; D010940:Plant Proteins; D020033:Protein Isoforms; D007073:Immunoglobulin E