Figure 2.

(a) Alignment of the deduced protein sequence of the bovine immunoglobulin A (IgA) Fc receptor (bFcαR) with those of CD89 and bFcγ2R. The GenBank accession numbers of nucleotide sequences of these three FcRs are AY247821, X54150 and Z37506, respectively. Identical residues are boxed in black, whereas conserved residues are in grey. The first amino acid of the mature bFcαR protein (Q-22) is indicated by ‘+1’ above the sequence. The four conserved extracellular cysteine residues that form the disulphide bonds of the two immunoglobulin domains are indicated (*). The four potential N-linked glycosylation sites are marked with a ‘+’. The putative transmembrane regions of all three FcRs are indicated by a dashed line above the sequence. (b) Close-up of the F–G loop regions of CD89, bFcαR and bFcγ2R. The residues of CD89 and bFcα2R, which have been shown to be important for binding to IgA and bIgG2, respectively, are indicated by arrows.