Affinity and kinetic analysis of P-selectin binding to P-selectin glycoprotein ligand-1

Leukocytes use the cell-surface mucin P-selectin glycoprotein ligand-1 (PSGL-1) to tether to and roll on P-selectin on activated endothelial cells and platelets. By using surface plasmon resonance, we measured the affinity and kinetics of binding of soluble monomeric human P-selectin to immobilized PSGL-1 from human neutrophils. Binding was specific, as documented by its Ca2+-dependence, its inhibition by specific monoclonal antibodies to P-selectin and PSGL-1, and its abrogation by treating PSGL-1 with sialidase, Similar binding was observed for soluble P-selectin that contained the lectin and epidermal growth factor domains plus all nine consensus repeats, and for a soluble construct that contained only the lectin and epidermal growth factor domains, Soluble P-selectin bound saturably to a single class of sites on PSGL-1 with a dissociation constant (K-d) of 320 +/- 20 nM, The measured k(off) was 1.4 +/- 0.1 s(-1), and the calculated k(on) was 4.4 x 10(6) M-1 s(-1). We conclude that monomeric P-selectin binds to PSGL-1 with fast association and dissociation rates and relatively high affinity. These features may be important for efficient tethering and rolling of leukocytes at physiologic densities of PSGL-1 and P-selectin.