The different modes of binding of the dust mite allergens, Der f 7 and Der p 7, on a monoclonal antibody WH9 contribute to the differential reactivity

Der f 7 and Der p 7 are important house dust mite allergens. An IgE-binding inhibition monoclonal antibody WH9 reacts ten folds stronger against Der p 7 than to Der f 7. The purpose of this study is to identify the antigenic determinant(s) and the structural basis of Der f 7 recognize by WH9. WH9-reactive determinant(s) on Der f 7 was identified by immunoblot and immunoblot inhibition. The 3-D binary complex structures of WH9 and the group 7 allergens were simulated with homology modeling and docking methods. WH9 reacted with the Der f 7 f9 fragment. Among the five site-directed Der f 7 mutants, WH9 showed reduced immunoblot reactivity against Der f 7 S156A, D159A and P160A mutants. Only the wild-type protein and the Der f 7 I157A and L158A mutants can inhibit significantly the WH9-binding against Der f 7. The structural model of the Der f 7-WH9 complex suggests residues S156 and D159 of Der f 7 can bind to WH9 via potential hydrogen bonds. The structure models of Der f 7-WH9 and Der p 7-WH9 complexes revealed that the differential modes of binding of Der p 7 and Der f 7 allergens on WH9 contribute to the differential reactivity of WH9 against the Der f 7 and the Der p 7 mite allergens.