Cell adhesion molecules (CAMs) known as Selectins (CD 62) are a family of CAMs that bind sugar polymers. Additionally, due to a similar amino terminus and calcium-dependent binding, Selectins belong within the category of C-type lectins and share a similar amino terminus with them. The cell membrane molecule known as a Selectin is made up of a series of consensus repeats (CR) domains, a transmembrane domain, an epidermal growth factor-like domain, an epidermal growth factor-like (EGF) domain, a short cytoplasmic tail, and an N-terminal calcium-dependent lectin domain (CRD) that is responsible for carbohydrate recognition. All three types of Selectins recognize the O-saccharide, N-saccharide, silanized, and fucosylated tetrasaccharide sialyl Lewis x (sLex) at the terminals of glycoproteins or glycolipids and their modifiers because all three types of Selectins have a carbohydrate recognition domain.
Fig.1 The 3-D structure of P-Selectin (purple), E-Selectin (red), and L-Selectin (green). (PDB)
Based on the cell type they were first time identified, the selectins family can be divided into three members:
P-Selectin is expressed by endothelial cells and megakaryocytes. By acting as a mediator, chemicals like thrombin, histamine, or complement swiftly redistribute P-Selectin to the plasma membrane.
The glycoprotein called E-Selectin is only expressed by endothelial cells (CD62E). E-Selectin is produced by skin and bone marrow microvessels on a constitutive basis.
These three Selectins contain an N-terminal lectin-like domain that can bind to carbohydrates efficiently, which has 120 amino acids sharing 60 to 70% identity. The adjacent EGF-like domains also share about 60% sequence identity. Followed by the CR domain, which has a variable number of 2-9 consensus repeats of approximately 60 amino acids in length, there are a short transmembrane domain and a cytoplasmic domain after the CR domain.
Fig.2 Schematic representation of P-, E-, and L- Selectin structures. (Tvaroška, et al., 2020)
Selectin interactions with their counter-receptors mediate their adhesion to other cellular or matrix components. Many common physiological activities, like the capacity of leukocytes to adhere to the endothelium and then extravasate to areas of inflammation or damage to treat wounds and fight infections, depend on Selectin binding interactions. The severity of inflammatory disorders is frequently correlated with elevated Selectin levels, and aberrant leukocyte homing to endothelial cells, which is mediated by P- and E-Selectin, is a major contributor to atherosclerosis. Selectin-ligand interactions have also been implicated in tumor progression and metastasis, so they can be regarded as targeted points for some Therapies.
Fig.3 Multistep leucocyte adhesion cascade. (Hassan, et al., 2020)
Due to Selectins especially binding carbohydrates, some tools like Microarray Platform, especially Glycan Microarray can be used to study the binding ability of Selectins. Moreover, CD BioGlyco provides one-stop services to help customers to study the roles of Selectins in human diseases. If you are interested in our services, please contact us for more detailed information.