Interactions of PSGL-1 with selectins

Summary form only received as follows: The selectins are membrane-anchored C-type lectins that enable flowing leukocytes to tether to and roll on the vessel wall, the first step in inflammation. Activated endothelial cells and/or platelets express E- and P-selectin, and leukocytes express L-selectin. P-selectin glycoprotein ligand-l (PSGL-1) is a disulfide-bonded homodimeric sialomucin on leukocytes that binds to all 3 selectins. P- and L-selectin bind to an N-terminal region of PSGL-1 that requires sulfation of at least one of 3 clustered tyrosines and attachment of a core-2, sialylated and fucosylated O-glycan to a specific threonine. PLI, a mAb that binds to this N-terminal region, blocks tethering and rolling of leukocytes on P-selectin and partially inhibits L-selectin-dependent leukocyte-leukocyte contacts that amplify leukocyte accumulation on vascular surfaces. A small N-terminal tryptic fragment of PSGL-1 or a small synthetic glycosulfopeptide comprising the N-terminal region binds with high affinity to P-selectin. Even after elimination of its single disulfide bond, PSGL-l forms noncovalent dimers on the cell surface that interact efficiently with P-selectin. To mediate leukocyte rolling under shear stress, selectin-ligand bonds must form and break rapidly, and they must also resist dissociation by applied force. Murine pre-B cells expressing P- or L-selectin roll on transfected CHO cells that co-express PSGL-1 with core 2 /spl beta/1,6-GlcNAc transferase and Fuc-TVII. Cells expressing Por L-selectin also roll on cells expressing PSGL-1 constructs with only one of the 3 tyrosines. However, the cells roll faster and skip more frequently because of increases in either the intrinsic koff or the reactive compliance of the selectin-PSGL-l bond. The degree of tyrosine sulfation, the type of glycosylation, and the specific amino acid sequence of the N-terminal glycosulfopeptide region of PSGL-1 may modulate the intrinsic biochemical properties or the mechanical properties of selectin bonds.