In shape--the art of mapping conformational epitopes.

ternative approach is the usage of filamentous phage libraries that display random sets of peptides. Panning of these libraries with the antibody of interest will select peptides that are involved in antibody-antigen interaction and that may mimic conformational B cell epitopes. The article of Tiwari et al. [4] in this issue describes the mapping of a conformational epitope on the major cockroach allergen Bla g 2. This mapping was performed by the panning of a 12-mer phage display peptide library (i.e. Ph.D. library purchased from the New England Biolabs) with the mAb 7C11 [5] that is described as a surrogate for human IgE. For this reason, a modified version of the panning protocol was established to select in a more stringent way for high-affinity binding phages. Only two displayed peptides could be identified that share very high degrees of amino acid identities as they differed in only one amino acid. The isolated phages displayed peptides with similar specificity and binding strength. Peptides were further matched on the surface of the threedimensional structure of Bla g 2 (PDB ID: 1YG9) with the help of the computational algorithm EpiSearch. In the present study, mapping of the two peptides led to the isolation of four overlapping surface patches that share four amino acids. The four patches identified 17 out of 18 experimentally determined residues; this corresponds to a discovery of 94%. The predicted conformational epitope In type I allergy, IgE antibodies directed against specific epitopes on foreign proteins or glycoproteins are produced during the process of sensitization. These IgE antibodies are further bound to effector cells like mast cells and basophils, and their crosslink through the corresponding allergens is essential for the initiation of allergic symptoms. The vast majority of allergens contain conformational B cell epitopes, comprising amino acids that are in close vicinity only in the folded protein whereas they are noncontinuous in the linear sequence. Resulting from this three-dimensional architecture, conformational epitopes are difficult to characterize. However, it is of great importance for the better understanding of immune responses and for the design of effective active and passive treatment strategies to gain also precise knowledge of the interacting surface between IgE antibodies and their corresponding epitopes. The most direct way of identifying conformational epitopes is still the determination of the three-dimensional structure of the antibody-allergen complex by Xray crystallography [1, 2] . But there are limitations in the performance as the procedure is very time consuming and needs a large amount of purified protein complexes. Another method is presented in the article of Gieras et al. [3] showing that peptide-specific monoclonal antibodies (mAb) can also map conformational IgE epitopes. An alPublished online: November 23, 2011