Complete structure of the mouse mast cell receptor for IgE (Fc ϵ RI) and surface expression of chimeric receptors (rat-mouse-human) on transfected cells

Abstract

The high affinity receptor for IgE (Fc ϵ RI) found on mast cells and basophils is a tetrameric complex of a single α subunit, a single β subunit, and two identical γ subunits. The genes for the three subunits of mouse Fc ϵ RI have now been cloned from the mast cell line, PT18. When compared at the DNA level, the rat and mouse subunits are similarly conserved. However, at the protein level the homology between mouse and rat α is surprisingly low (71% identities) especially in the cytoplasmic regions (57% identities) which are of different length (25 and 20 residues, respectively). By contrast the β and γ are homogeneously conserved between mouse and rat (83 and 93% identities, respectively). The consensus amino acid sequence of the α subunit derived from three species (rat, mouse, and human) shows that the cytoplasmic tail diverges to the same extent as the leader peptide. Conversely, the transmembrane domain of the α is highly conserved and contains 10 consecutive residues that are identical. Comparisons between mouse Fc ϵ RI and other mouse proteins reveal regions of high homology between the α subunit and Fc γ RIIa and between the γ subunit and the ζ chain of the T cell receptor. Cells transfected with the α gene express the α subunit on their surface very inefficiently. Efficient expression is only achieved after co-transfection of the three rodent genes or of the human α gene together with the rodent γ without apparent need for β. The subunits are completely interchangeable upon transfection so that various chimeric mouse-rat-human receptors can be expressed.