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Identification of a novel cat allergen--cystatin
K Ichikawa1, L D Vailes, A Pomés
1Asthma and Allergic Diseases Center, University of Virginia, Charlottesville 22901, USA.
Background:
Cat allergen is an important cause of sensitization among children with asthma in Japan. Although there is good evidence that cats produce other allergens, only one major allergen, Fel d 1, has been studied in detail.
Aims:
To identify and define the molecular structure of the other potential cat allergens.
Methods:
A cat skin cDNA library was screened using IgE antibodies to cat dander and selected clones were sequenced and expressed.
Results:
One cDNA clone contained an open reading frame encoding a 98-amino acid residue protein. Sequence homology searches revealed a high degree of identity with bovine and human cystatin A, 79 and 75%, respectively. This cat cystatin clone contained the conserved cysteine protease motif and two of three lipocalin motifs. By plaque immunoassay, 60-90% of cat allergic sera had IgE Ab to cat cystatin. This cysteine protease inhibitor motif was partially conserved in dog allergens, Can f 1 and Can f 2, which are lipocalins. Recombinant cystatin was produced in Escherichia coli cells and purified as an 11-kD protein, corresponding to the predicted MW of cystatin. The structure of cat cystatin was modeled on human cystatin B using the SWISS-MODEL.
Conclusion:
A newly identified allergen, cystatin, has been cloned from cat skin and is a member of the cysteine protease inhibitor family.