Use of domain-swapped molecules for conformational epitope mapping of desmoglein 3 in pemphigus vulgaris

Pemphigus vulgaris is an autoimmune blistering disease caused by autoantibo dies against desmoglein 3, a member of the desmosomal cadherin family. Thes e autoantibodies recognize conformation-dependent epitopes on desmoglein 3. In this study we attempted to map the conformational epitopes of desmoglei n 3 in pemphigus vulgaris using recombinant desmoglein 3 produced by the ba culovirus expression system. We developed a series of domain-swapped molecu les between desmoglein 3 and desmoglein 1, which have similar structures bu t distinct epitopes. These were developed by substituting deleted segmental regions of desmoglein 3 by the corresponding desmoglein 1. Thus domain-swa pped molecules containing desmoglein 3 residues 1-403, 1-161, 163-566, and 405-566 were constructed and used as competitors for competition enzyme-lin ked immunosorbent assay against the entire extracellular domain of desmogle in 3 with 25 pemphigus vulgaris sera. Considering more than 50% absorption as significant, residues 1-403 and 1-161 showed significant absorption in 2 4 out of 25 (96%) and 18 out of 25 (72%) pemphigus vulgaris sera, respectiv ely, whereas only one serum and no sera showed significant absorption by re sidues 163-566 and 405-566, respectively. Furthermore, no apparent change i n their major epitopes was seen during the time course in four pemphigus vu lgaris cases tested. These findings indicate that the domain-swapping appro ach is useful for conformational epitope mapping in pemphigus and that amin o-terminal residues 1-161, which are considered to include a region essenti al for cell-cell adhesion in cadherins, contain the critical residues of th e conformational epitope of desmoglein 3 recognized by the autoantibodies i n pemphigus vulgaris sera.