Figure 1.
Nomenclature and key structural characteristics of human Siglecs. Although 15 are shown, Siglec-13 is present in nonhuman primates but not in man. V structures indicate the arginine-containing V-set domains with lectin activity; these are followed by C2-type Ig repeat domains. U-shaped structures for Siglec-XII indicate the mutated V-set domains missing arginine that have lost their lectin activity. Also shown is DAP12, illustrated as a shorter transmembrane structure co-associating with Siglec-13, Siglec-14, and Siglec-15. See key for symbols representing cytoplasmic signaling motifs.