Distinct binding kinetics of E‐, P‐ and L‐selectins to CD44

Molecular‐level selectin‐cluster of differentiation 44 (CD44) interactions are far from clear because of the complexity and diversity of CD44 glycosylation and isoforms expressed on various types of cells. By combining experimental measurements and simulation predictions, the binding kinetics of three selectin members to the recombinant CD44 were quantified and the corresponding microstructural mechanisms were explored, respectively. Experimental results showed that the E‐selectin–CD44 interactions mainly mediated the firm adhesion of microbeads under shear flow with the strongest rupture force. P‐ and L‐selectins had similar interaction strength but different association and dissociation rates by mediating stable rolling and transient adhesions of microbeads, respectively. Molecular docking and molecular dynamics (MD) simulations predicted that the binding epitopes of CD44 to selectins are all located at the side face of each selectin, although the interfaces denoted as the hinge region are between lectin and epidermal growth factor domains of E‐selectin, Lectin domain side of P‐selectin and epidermal growth factor domain side of L‐selectin, respectively. The lowest binding free energy, the largest rupture force and the longest lifetime for E‐selectin, as well as the comparable values for P‐ and L‐selectins, demonstrated in both equilibration and steered MD simulations, supported the above experimental results. These results offer basic data for understanding the functional differences of selectin–CD44 interactions. We explored the distinct binding kinetics of three selectin members to cluster of differentiation 44 (CD44). Using E‐/P‐/L‐selectin‐functionalized microbeads and CD44‐physisorbed substrate in a flow chamber assay that mimics the in vivo cellular adhesion under blood flow, we found that the strongest E‐selectin–CD44 interactions mediated the firm adhesion of microbeads, the intermediate P‐selectin–CD44 interactions mediated two phases of both rolling and firm adhesion, and the weakest L‐selectin–CD44 interactions mediated tethering adhesions with short‐lived stopping.