An IgE-binding protein with a distinctive repetitive sequence and homology with an IgG receptor

Proteins that bind IgE play important roles in both the synthesis and function of IgE are therefore intimately involved in IgE-mediated human allergic disorders. This report describes the structure of an IgE-binding protein, as predicted from sequencing a cDNA cloned from rat basophilic leukemia cells. This protein contains two domains: the amino-terminal domain (140 amino acids) consists of a highly conserved repetitive amino acid sequence, Tyr-Pro-Gly-Pro/Gln-Ala/Thr-Pro/Ala-Pro-Gly-Ala, whereas the carboxyl-terminal domain (122 amino acids) shares significant sequence homology with a domain of lymphocyte/macrophage receptor for the Fc portion of IgG. Other proteins with this type of structure but with affinity for other immunoglobulin isotypes may exist and may represent a heretofore unidentified component of the immune system.