Figure 1.

FcγR III/CD16 is expressed in two forms from two distinct genes. A and B, FcγRIIIb/CD16b is highly expressed on neutrophils, and FcγRIIIa/CD16a is the predominant FcγR expressed on NK cells. B, these proteins differ by only four amino acid residues (highlighted in yellow) in the mature proteins. The N-terminal signal peptide is indicated in red and is not found in the fully processed proteins. The C-terminal residues of CD16b shown in orange are cleaved prior to addition of the glycosylphosphatidylinositol anchor at the newly uncovered C-terminal serine. N-glycosylation sites are indicated with gray shading. Both proteins are cleaved by ADAM17 and released from the cell surface following cell activation. Resolved N-glycan residues are shown as spheres.