Comparative analysis of the genes encoding group 3 allergens from Dermatophagoides pteronyssinus and Dermatophagoides farinae

Group 3 allergens of the genus Dermatophagoides represent one of the major groups of house dust mite allergens. The cDNA sequence data for Der p 3, in combination with both N-terminal amino acid sequences and substrate affinity data, have confirmed that the group 3 allergens are trypsin-like proteases. Using the information from the Der p 3 P3WS1 cDNA clone, genes encoding both Der f3 and Der p 3 have now been amplified by the polymerase chain reaction and analysed. Two Der f3 clones and three Der p 3 genomic clones were sequenced. Each of the clones contained a single small intron and encoded a mature protein of 233 amino acids. The nucleotide sequence was identical for both Der f3 clones. There was 81% identity between the Der f3 sequence and the original Der p 3 P3WS1 clone. The calculated molecular weight of Der f3 was 25.27 kDa compared to 24.98 kDa for Der p 3. All the amino acid residues required for the catalytic activity and the substrate specificity were conserved between the two homologues. The coding sequences of two of the three Der p 3 genomic clones were identical to the original Der p 3 P3WS1 clone with the third having nucleotide changes resulting in four non-conservative amino acid substitutions in the mature protein. These substitutions resulted in a molecule with a slightly larger molecular weight and a more acidic pi value than the original Der p 3 clone. This third Der p 3 genomic clone is, therefore, an isoform of the Der p 3 P3WS1 clone and is classified as an isovariant of the allergen. The nucleotide sequence data presented are the first reported for Der f3. The Der f3 gene, like the Der p 3 gene, encoded a trypsin-like protease, but with a slightly larger molecular weight.