Sialoadhesin is a cell adhesion molecule found on the surface of certain cells of the immune system called macrophages. It is found in especially high amounts on macrophages of the spleen, liver, lymph node, bone marrow, colon, and lungs. Also, in patients suffering from rheumatoid arthritis, the protein has been found in great amounts on macrophages of the affected tissues. It is defined as an I-type lectin, since it contains 17 immunoglobulin (Ig) domains (one variable domain and 16 constant domains), and thus also belongs to the immunoglobulin superfamily (IgSF). Sialoadhesin binds to certain molecules called sialic acids. During this binding process a salt bridge (protein) is formed between a highly conserved arginine residue (from the v-set domain to the 3'-sialyllactose) and the carboxylate group of the sialic acid. Since sialoadhesin binds sialic acids with its N-terminal IgV-domain, it is also a member of the SIGLEC family. Alternate names for sialoadhesin include siglec-1 and CD169 (cluster of differentiation 169).
Sialaodhesin (CD169) positive macrophages, along with mesenchymal stem cells and beta-adrenergic neurons, form the hematopoietic stem cell niche in the bone marrow. CD169+ macrophages mediate signaling between the various cells and seem to promote hematopoietic stem cell retention to the niche.
^PDB: 2BVE; Zaccai NR, May AP, Robinson RC, Burtnick LD, Crocker PR, Brossmer R, Kelm S, Jones EY (February 2007). "Crystallographic and in silico analysis of the sialoside-binding characteristics of the Siglec sialoadhesin". J. Mol. Biol.365 (5): 1469–79. doi:10.1016/j.jmb.2006.10.084. PMID17137591.
^ abHartnell A, Steel J, Turley H, Jones M, Jackson DG, Crocker PR (January 2001). "Characterization of human sialoadhesin, a sialic acid binding receptor expressed by resident and inflammatory macrophage populations". Blood97 (1): 288–96. doi:10.1182/blood.V97.1.288. PMID11133773.
^Varki A (2001-09-10). "Sialoadhesin, Siglec-1 (CD169)". Protein Reviews on the Web (PROW) Guide. United States National Center for Biotechnology Information (NCBI). Retrieved 2011-04-15.
^Kelm S, Pelz A, Schauer R, Filbin M, Tang S, de Bellard M, Schnaar R, Mahoney J, Hartnell A, Bradfield P (1994). "Sialoadhesin, myelin-associated glycoprotein and CD22 define a new family of sialic acid-dependent adhesion molecules of the immunoglobulin superfamily". Curr Biol4 (11): 965–72. doi:10.1016/S0960-9822(00)00220-7. PMID7533044.