Role of FcαR EC2 region in extracellular membrane localization.

The FcαR receptor (CD89) binds to the constant region of Immunoglobulin (Ig) A to mediate mucosal immunity [1-2]. FcαR consist of five exons: two that code for the signal peptide regions S1 & S2, two for the extracellular regions EC1 and EC2, and the final exon for the transmembrane/cytoplasmic tail region [3]. Previously, we reported that the EC1 region plays an essential role for extracellular membrane localization of the receptor [4], where the absence of EC1 would prevent the variants from localizing to the cell surface, even with a full signal peptide. In the case of FcαR Variant 4 (lacking the S2 region only), there was some "leakiness" to membrane surface localization.