Identification of residues in the first domain of human Fcα receptor essential for interaction with IgA

Abstract

The FcR family contains multiple receptors for Igs, of which the most distantly related (~20%) is the IgA receptor (human FcαR), being more homologous (~35%) to another family of killer-inhibitory receptor-related immunoreceptors with a 19q13.4 chromosomal location in humans. This study of the FcαR demonstrated that, like several IgG receptors, FcαR is a low affinity receptor for Ab (K(a) ~ 106 M-1). Rapid dissociation of the rsFcαR:IgA complex (t(1/2) ~ 25 s) suggests that monomer IgA would bind transiently to cellular FcαRs, while IgA immune complexes could bind avidly. Mutagenesis of histidyl 85 and arginyl 82, in the FG loop of domain 1, demonstrated that these residues were essential fo..