Identification of a novel cat allergen--cystatin.
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.


OBJECTIVE
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.


CONCLUSIONS
A newly identified allergen, cystatin, has been cloned from cat skin and is a member of the cysteine protease inhibitor family.
Ichikawa
K
K
Asthma and Allergic Diseases Center, University of Virginia, Charlottesville 22901, USA.
Vailes
L D
LD
Pomés
A
A
Chapman
M D
MD
D000485:Allergens / Q000235:genetics / Q000276:immunology; D000818:Animals; D052179:Antigens, Plant; D002415:Cats / Q000276:immunology*; D002417:Cattle; D003001:Cloning, Molecular; D015891:Cystatins / Q000235:genetics* / Q000276:immunology*; D004285:Dogs; D006801:Humans; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
D000485:Allergens; D052179:Antigens, Plant; D015891:Cystatins; C110827:allergen Can f 2; C091462:allergen Can f I