Lectins
Carbohydrate-binding proteins (lectins) have roles to play in many important processes such as self/non-self recognition, endocytosis, routing and chaperoning of molecules within the cell, and trafficking of cells within the body. C-type lectins, including CL-P1, the monocyte mannose receptor (MMR), mannose binding lectin (MBL), ficolins, and others are active in pathogen recognition. Dendritic cell C-type lectins, such as DC-SIGN, DC-SIGNR, DCAR, DCIR, Dectins, and DLEC, are important in dendritic cell trafficking and formation of the immunological synapse. The selectins are also well known for mediating cell trafficking.
R&D Systems offers a range of research tools for the study of these lectin subgroups, as well as sialic acid-binding Ig-type lectins (siglecs) and galactose-binding lectins (galectins).
Galectins
The galectins constitute a large family of carbohydrate-binding proteins that function in many systems both intracellularly and following secretion. Galectins contain either one or two carbohydrate recognition domains (CRR) which mediate recognition of N-acetyl-lactosamine-containing glycoproteins. Some galectins exist in multiple isoforms due to alternative splicing. Individual galectins differ in their tissue distribution and in their carbohydrate-binding specificities.
| Galectin-1 | Galectin-2 | Galectin-3 | Galectin-3BP/MAC-2BP |
| Galectin-4 | Galectin-7 | Galectin-8 | Galectin-9 |
| Galectin-10 | Galectin-12 | Galectin-14 | Galectin-3C |
Ig-type Lectins
Similar to antibodies and T-cell receptors, Ig-type lectins mediate glycan recognition via an immunoglobulin (Ig)-like domain. The major homologous subfamily of Ig-type lectins are called Siglecs (sialic acid (Sia)-recognizing Ig-superfamily lectins). The Siglecs can be broadly classified into two subgroups: Siglecs-1, -2, and -4, and a Siglec-3/CD33-related subgroup (Siglecs-3, and -5 through -13 in primates) defined by sequence similarity and clustered gene localization. They are widely expressed on hematopoietic cells, often in a cell-type-specific manner. Siglec-4/MAG is a myelin component in Schwann cells and oligodendrocytes. Their ligands, sialic acids, are negatively charged monosaccharides found on cell-surface glycoproteins and glycolipids. Although Siglec functions continue to be defined, most have intracellular immunoreceptor tyrosine-based inhibitory motifs (ITIM), implicating them in the suppression of immunoreceptor signaling. Siglecs may also participate in cell/cell interactions or act as receptors for the entry of viral or bacterial pathogens.
Selectins
The Selectin family is comprised of three members, E-Selectin, L-Selectin, and P-Selectin. E-Selectin (endothelial leukocyte adhesion molecule-1, ELAM-1, CD62E) is transiently expressed on vascular endothelial cells in response to IL-1 beta and TNF-alpha. The human and rat proteins share approximately 67% amino acid sequence identity. The mouse and rat proteins share approximately 78% amino acid sequence identity. L-Selectin (Leukocyte Selectin, LAM-1, LECAM-1, LECCAM-1, TQ1, Leu-8, MEL-14 antigen, DREG, lymph node homing receptor, CD62L) is expressed constitutively on a wide variety of leukocytes. Two forms of L-Selectin have been reported, apparently arising as a result of post-translational modifications. Human and mouse L-Selectin share 76% amino acid sequence identity. Human P-Selectin (GMP-140, LECAM-3, PADGEM, CD62P) is expressed by activated platelets and endothelial cells. The extracellular domains of human and mouse P-Selectin share approximately 73% amino acid sequence identity.
| E-Selectin/CD62E | E-Selectin (CD62E)/P-Selectin (CD62P) | L-Selectin/CD62L | P-Selectin/CD62P |
Other Lectins
| Intelectin-1/Omentin | Intelectin-1/2 | Intelectin-1/2 |