Identification and Characterisation of Two Allergens from the Dust Mite Acarus siro, Homologous with Fatty Acid–Binding Proteins

Abstract

Background: Dust mites are a major cause of allergic disease worldwide. The dust mite Acarus siro is an inducer of occupational allergy among farmers, but sensitisation has also been found in non–farming populations. Methods: A degenerate primer was designed to the N–terminal amino acid sequence of a 15–kD IgE–binding protein in A. siro extract. The cDNA sequence was obtained by using reverse transcriptase polymerase chain reaction, standard cloning and sequencing techniques. The protein was expressed in Escherichia coli with a 6–histidine tag at its C–terminus. Immunoblotting of the recombinant protein and whole extract was performed using patient sera. Results and conclusion: 15 and 17–kD allergens were identified in a fraction of A. siro extract. The cDNA of the 15–kD allergen was isolated, cloned and sequenced and the allergen was expressed as a recombinant protein. The calculated molecular weight of the cDNA–encoded protein is 14.2 kD. The predicted amino acid sequence has one potential N–glycosylation site at position 4–6 and a cytosolic fatty acid–binding protein signature at position 5–22. The protein has 64% sequence identity with Blo t 13, an allergen from the dust mite Blomia tropicalis, as well as homology with several other fatty acid–binding proteins (FABPs) from different organisms. The allergen was named Aca s 13 and was recognised strongly by 3 of 13 (23%) of the subjects investigated. The amino acid sequence of the 17–kD protein was partly determined and it also showed high sequence homology with Blo t 13 and FABPs.