FIGURE 2.

Structural and sequence comparisons among Fc receptors. A, shown is a comparison of the hinge angle between FcγRI and other FcRs, including FcγRIIa, FcγRIIb, FcγRIII, and FcϵRI. All structural superpositions of the receptor were based on the D2 domain alignment. The hinge angles were calculated using Hinge program. The FcϵRI and FcγRIII residues involved in Fc contact interface are displayed on their receptor structures together with the putative ligand binding residues of FcγRI. B, shown is sequence alignment of the ectodomain of FcRs. The secondary structure elements (arrow for β–strands and cylinder for helices) are indicated above the sequence. The glycosylation sites in FcγRI are indicated by asterisks. The D1-D2 and D2-D3 interface residues in FcγRI are shaded in yellow and purple, respectively. The conserved pair-wise D1-D2 interactions among FcγRI and FcϵRI are highlighted in black boxes. The Fc-contacting residues in FcγRIII are shaded in red.