Crystal structure and epitope analysis of house dust mite allergen Der f 21

Abstract

Group 21 and 5 allergens are homologous house dust mite proteins known as mid-tier allergens. To reveal the biological function of group 21 allergens and to understand better the allergenicity of the rDer f 21 allergen, we determined the 1.5 Å crystal structure of rDer f 21 allergen from Dermatophagoides farinae. The rDer f 21 protein consists of a three helical bundle, similar to available structures of group 21 and homologous group 5 allergens. The rDer f 21 dimer forms a hydrophobic binding pocket similar to the one in the Der p 5 allergen, which indicates that both of the homologous groups could share a similar function. By performing structure-guided mutagenesis, we mutated all 38 surface-exposed polar residues of the rDer f 21 allergen and carried out immuno-dot blot assays using 24 atopic sera. Six residues, K10, K26, K42, E43, K46, and K48, which are located in the region between the N-terminus and the loop 1 of rDer f 21 were identified as the major IgE epitopes of rDer f 21. Epitope mapping of all potential IgE epitopes on the surface of the rDer f 21 crystal structure revealed heterogeneity in the sIgE recognition of the allergen epitopes in atopic individuals. The higher the allergen-sIgE level of an individual, the higher the number of epitope residues that are found in the allergen. The results illustrate the clear correlation between the number of specific major epitope residues in an allergen and the sIgE level of the atopic population.

Hydrophobic ligands influence the structure, stability, and processing of the major cockroach allergen Bla g 1

“…However, studies on the human albumins reveal that only 0.5–2 of these sites are occupied under physiological conditions suggesting that lipids bind to the shallow, surface-exposed cavities of albumins with low affinity and in rapid exchange with the solution, consistent with the physiological role of these allergens as transport proteins 36–38 . In the case of the group 5 mite allergens, crystal studies of Der p 5 and its homologue Der f 21 reveal a helical bundle which can assemble into a dimeric structure, the interface of which encloses a 3000 ų cavity 39,40 . While the size of this cavity is comparable to that of Bla g 1, docking studies along with crystal structures of the related allergen Der f 21 reveal an average occupancy of only a single fatty-acid or PEG detergent molecule 39,41 .…”

IgE-binding residues analysis of the house dust mite allergen Der p 23

“…The ratio of solvent-accessible surface area (ASA) to the calculated Gly-X-Gly (GXG) tripeptide value for all the residues was obtained. Previous IgE epitope mapping of dust mite allergens from groups 5, 13, and 21 found that the major IgE-binding epitopes consist of polar and charged residues 10 , 12 , 15 , 16 . Hence, we identified all solvent-accessible, polar and charged residues (17 in total) on the surface of Der p 23, and mutated these residues to alanine to produce a set of 17 single-residue mutants.…”

“…S6 ). The immunoassay and the analysis of experimental data performed in this study have been previously used and validated in multiple other publications 12 , 15 , 16 , 25 . D56A mutant was however excluded from the analysis due to the high background in negative controls.…”

“…Sera with increased Der p 2-sIgE titers were shown to correlate with the increased complexity of the IgE repertoires 17 . A comprehensive IgE epitope screening using all the surface-exposed residues of rDer f 21 (group 21 allergen) from D. farinae has highlighted the positive correlation between the number of IgE-binding residues and rDer f 21-sIgE level 15 . While IgE antibody binding to an increasing number of IgE-binding residues has been associated with sIgE level, the information regarding the clinical significance of the number of IgE-binding residues remained to be identified.…”

Ole e 15 and its human counterpart -PPIA- chimeras reveal an heterogeneous IgE response in olive pollen allergic patients

“…Several IgE-binding studies of Bet v 1 36,37 , Der p 2 47,48 and other allergens 49,50 have revealed that the allergen-specific IgE-repertoire can be very complex in terms of IgE-clonality, affinity and concentration. Besides, it is well-known that these parameters affect effector cell degranulation, which is only triggered in the presence of at least two IgE-clones binding non-overlapping epitopes on the allergen surface 51 .…”