Characterization of the ligand binding site of the bovine IgA Fc receptor (bFcαR)

Recently, we identified a bovine IgA Fc receptor (bFcαR), which shows high homology to the human myeloid FcαR, CD89. IgA binding has previously been shown to depend on several specific residues located in the B-C and F-G loops of the membrane-distal extracellular domain 1 of CD89. To compare the ligand binding properties of these two FcαRs, we have mapped the IgA binding site of bFcαR. We show that, in common with CD89, Tyr-35 in the B-C loop is essential for IgA binding. However, in contrast to earlier observations on CD89, mutation of residues in the F-G loop did not significantly inhibit IgA binding.