Surface-bound selectin_ligand binding is regulated by carrier diffusion

摘要

Two-dimensional (2D) kinetics of receptor_ligand interactions governs cell adhesion in many biological processes. While the dissociation kinetics of receptor_ligand bond is extensively investigated, the association kinetics has much less been quantified. Recently receptor_ligand interactions between two surfaces were investigated using a thermal fluctuation assay upon biomembrane force probe technique (Chen et al. in Biophys J 94:694-701, 2008). The regulating factors on association kinetics, however, are not well characterized. Here we developed an alternative thermal fluctuation assay using optical trap technique, which enables to visualize consecutive binding_unbinding transition and to quantify the impact of micro-bead diffusion on receptor_ligand binding. Three selectin constructs (sLs, sPs, and PLE) and their ligand P-selectin glycoprotein ligand 1 were used to conduct the measure_ments. It was indicated that bond formation was reduced by enhancing the diffusivity of selectin-coupled carrier, sug_gesting that carrier diffusion is crucial to determine receptor_ligand binding. It was also found that 2D forward rate predicted upon first-order kinetics was in the order of sPs > sLs > PLE and bond formation was history-depen_dent. These results further the understandings in regulating association kinetics of surface-bound receptor_ligand interactions.