SIGLEC

SIGLECs, short for "sialic acid binding Ig-like lectins" are cell surface receptors and members of the immunoglobulin superfamily (IgSF) that recognize sugars. Their ability to recognize carbohydrates using an immunoglobulin domain places them in the group of I-type (Ig-type) lectins. They are transmembrane proteins that contain an N-terminal V-like immunoglobulin (IgV) domain that binds sialic acid and a variable number of C2-type Ig (IgC2) domains. [cite journal |author=Crocker P, Clark E, Filbin M, Gordon S, Jones Y, Kehrl J, Kelm S, Le Douarin N, Powell L, Roder J, Schnaar R, Sgroi D, Stamenkovic K, Schauer R, Schachner M, van den Berg T, van der Merwe P, Watt S, Varki A |title=Siglecs: a family of sialic-acid binding lectins |journal=Glycobiology |volume=8 |issue=2 |pages=v |year=1998 |pmid=9498912] [ [http://www.genenames.org/genefamily/siglec.html Siglecs ] ]

The first described Siglec is sialoadhesin (Siglec-1/CD169) that is a lectin-like adhesion molecule on macrophages. [cite journal |author=Crocker P, Gordon S |title=Properties and distribution of a lectin-like hemagglutinin differentially expressed by murine stromal tissue macrophages |journal=J Exp Med |volume=164 |issue=6 |pages=1862–75 |year=1986 |pmid=3783087 |doi=10.1084/jem.164.6.1862] Other Siglecs were later added to this family, including CD22 (Siglec-2), which is restricted to B cells and has an important role in regulating their adhesion and activation, [cite journal |author=Stamenkovic I, Seed B |title=The B-cell antigen CD22 mediates monocyte and erythrocyte adhesion |journal=Nature |volume=345 |issue=6270 |pages=74–7 |year=1990 |pmid=1691828 |doi=10.1038/345074a0] CD33 (Siglec-3) and myelin-associated glycoprotein (MAG/Siglec-4).cite journal |author=Crocker P, Varki A |title=Siglecs in the immune system |journal=Immunology |volume=103 |issue=2 |pages=137–45 |year=2001 |pmid=11412300 |doi=10.1046/j.0019-2805.2001.01241.x] Several additional Siglecs (Siglecs 5–12) have been identified in humans that are highly similar in structure to CD33 so are collectively referred to as ‘CD33-related Siglecs’. [cite journal |author=Foussias G, Taylor S, Yousef G, Tropak M, Ordon M, Diamandis E |title=Cloning and molecular characterization of two splice variants of a new putative member of the Siglec-3-like subgroup of Siglecs |journal=Biochem Biophys Res Commun |volume=284 |issue=4 |pages=887–99 |year=2001 |pmid=11409877 |doi=10.1006/bbrc.2001.5052] [cite journal |author=Angata T, Kerr S, Greaves D, Varki N, Crocker P, Varki A |title=Cloning and characterization of human Siglec-11. A recently evolved signaling that can interact with SHP-1 and SHP-2 and is expressed by tissue macrophages, including brain microglia |journal=J Biol Chem |volume=277 |issue=27 |pages=24466–74 |year=2002 |pmid=11986327 |doi=10.1074/jbc.M202833200] CD33-related siglecs all have two conserved immunoreceptor tyrosine-based inhibitory motif (ITIM)-like motifs in their cytoplasmic tails suggesting their involvement in cellular activation.

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