FIGURE 3-1 Glycans play diverse roles within biological systems. SOURCE: Reprinted from Hart and Copeland 2010, with permission from Elsevier.
able to bind tightly to glycoprotein receptors, called integrins, which can lead to penetration of the endothelial cell monolayer and its basement membrane. The mechanisms for the initial binding and rolling of leukocytes have been studied extensively and involve transient expression of highly regulated glycan-binding proteins, called selectins, that decorate the surfaces of leukocytes, activated platelets, and activated endothelial cells. Selectins are exquisitely specific at binding to certain glycan structures. One of the primary determinants for their binding specificity is the tetrasaccharide known as sialyl Lewis x. The unique properties of the interactions between a selectin protein and its specific glycan ligand are critical to slowing leukocytes down so that they can bind to and then extravasate into inflamed tissue. Selectins and their glycan ligands also play a role in tumor metastasis (Dube and Bertozzi 2005; Laubli and Borsig 2010; St Hill 2011).