Analysis of the structure and allergenicity of recombinant pro- and mature Der p 1 and Der f 1: Major conformational IgE epitopes blocked by prodomains (1)
Group 1 allergens (Der p 1 and Der f 1) are the most clinically relevant allergen proteins because they exist in abundance in mite fecal pellets and account for more than 50% of IgE antibodies against total mite extract. Mature Der p 1 and Der f 1 have 82% sequence homology with each other. Synthetic peptides and recombinant fragments expressed in Escherichia coli show little or no IgE-binding activity compared with that of natural allergens.
The sizes of the recombinant mature forms without N-glycosylation and the natural types, which have a theoretic molecular weight of 25 kd, were identical to each other and estimated to be 17 to 18 kd.
Close correlations of IgE binding between the recombinant mature forms and natural types and between Der p 1 and Der f 1 were observed.
A paired t test showed significant differences in the inhibition assays between the proforms and recombinant mature forms and between the proforms and natural types.
Three to 10 times concentrations of the proforms relative to the recombinant mature forms were needed to exhibit the same histamine release response.
The Der f 1 prosegment consisted of an N-terminal domain-structure followed by a C-terminal extended loop. The prosegment was tightly anchored at 2 regions of the mature enzyme, the prosegment binding loop and the substrate binding cleft surrounding the catalytic residue Cys35. Asn53, the potential N-glycosylation site in mature Der f 1, was located on the surface distant from the catalytic site and the prosegment.
Because at least 12 isoforms with different amino acid sequences for Der p 1 and 2 for Der f 1 have been identified, patients could be sensitized to different isoforms by the environment. Phage peptides screened with an inhibitory anti-Der p 1 mouse mAb had a sequential motif in common with a Der p 1 sequence 147-160.