A modeling study of the alpha-subunit of human high-affinity receptor for immunoglobulin-E

The extracellular portion of the alpha-subunit of human high-affinity receptor for immunoglobulin-E (IgE), which contains two immunoglobulin (Ig) domains, was modeled on the basis of sequence similarity with antibody domains of known three-dimensional structure. Each receptor domain contains 86 amino acid residues, and both domains were modeled as bilayer structures. In both domains, one layer is made up of three anti-parallel beta-strands and the other of four strands, with the two layers linked by a disulfide bridge. The two domains show significant sequence similarity with each other (22 identities) and with the homologous domains of the murine and rat high-affinity receptors for IgE and the Fc gamma receptors from various species. Two plausible modes of association of the domains were considered: In the first, the two domains were positioned end-to-end, with essentially only longitudinal interactions between them; in the second, the molecule is more bent, with more lateral interactions between the two domains. The models will be useful in the design of protein engineering studies of this and homologous receptors to delineate the site of interaction with ligand. Furthermore, they may lend themselves as possible probes in crystallographic analyses by molecular replacement techniques.