AP BIOLOGY

Detailed explanation-1: -The selectins participate exclusively in heterophilic cell-cell binding because they have a lectin-like domain at their NH2 terminus that binds to specific carbohydrate residues on the opposite cell surface (see Figs.

Detailed explanation-2: -The selectins are a family of heterophilic CAMs that are dependent on fucosylated carbohydrates, e.g., mucins for binding.

Detailed explanation-3: -Selectins are carbohydrate-binding transmembrane proteins expressed on platelets (P-selectins), leukocytes (L-selectins) and endothelial cells (E-and P-selectins). Their role is to mediate the first steps of the recruitment of leukocytes from the blood stream in a series of pathologic situations [51].

Detailed explanation-4: -The cell-cell adhesions mediated by both selectins and integrins are heterophilic (see Figure 19-26): selectins bind to specific oligosaccharides on glycoproteins and glycolipids, while integrins bind to specific proteins.

Detailed explanation-5: -The selectins have characteristic extracellular regions composed of an amino-terminal lectin domain that binds a carbohydrate ligand, an epidermal growth factor-like domain, and two to nine short repeat units homologous to domains found in complement binding proteins.