Tyrosine replacement in P-selectin glycoprotein ligand-1 affects distinct kinetic and mechanical properties of bonds with P- and L-selectin

摘要

Selectins are adhesion molecules that initiate tethering androlling of leukocytes on the vessel wall. Rolling requires rapidformation and breakage of selectin–ligand bonds that must havemechanical strength to resist premature dissociation by the forcesapplied in shear flow. P- and L-selectin bind to the N-terminal regionof P-selectin glycoprotein ligand-1 (PSGL-1), a mucin on leukocytes. Todefine determinants on PSGL-1 that contribute to the kinetic andmechanical properties of bonds with selectins, we compared rolling oftransfected preB cells expressing P- or L-selectin on transfected cellmonolayers expressing wild-type PSGL-1 or PSGL-1 constructs withsubstitutions in targeted N-terminal residues. Rolling through P- orL-selectin required a Thr or Ser at a specific position on PSGL-1, theattachment site for an essential O-glycan, but required only one ofthree nearby Tyr residues, which are sites for Tyr-SO3formation. The adhesive strengths and numbers of cells rolling throughP- or L-selectin were similar on wild-type PSGL-1 and on each of thethree PSGL-1 constructs containing only a single Tyr. However, thecells rolled more irregularly on the single-Tyr forms of PSGL-1.Analysis of the lifetimes of transient tethers on limiting densities ofPSGL-1 revealed that L-selectin dissociated faster from single-Tyr thanwild-type PSGL-1 at all shears examined. In sharp contrast, P-selectindissociated faster from single-Tyr than wild-type PSGL-1 at highershear but not at lower shear. Thus, tyrosine replacements in PSGL-1affect distinct kinetic and mechanical properties of bonds with P- andL-selectin.