Stabilization of the Hinge Region of Human E-selectin Enhances Binding Affinity to Ligands Under Force

INTRODUCTION: E-selectin is a member of the selectin family of cell adhesion molecules expressed on the plasma membrane of inflamed endothelium and facilitates initial leukocyte tethering and subsequent cell rolling during the early stages of the inflammatory response via binding to glycoproteins expressing sialyl Lewis(X) and sialyl Lewis(A) (sLe(X/A)). Existing crystal structures of the extracellular lectin/EGF-like domain of E-selectin complexed with sLe(X) have revealed that E-selectin can exist in two conformation states, a low affinity (bent) conformation, and a high affinity (extended) conformation. The differentiating characteristic of the two conformations is the interdomain angle between the lectin and the EGF-like domain. METHODS: Using molecular dynamics (MD) simulations we observed that in the absence of tensile force E-selectin undergoes spontaneous switching between the two conformational states at equilibrium. A single amino acid substitution at residue 2 (serine to tyrosine) on the lectin domain favors the extended conformation. RESULTS: Steered molecular dynamics (SMD) simulations of E-selectin and PSGL-1 in conjunction with experimental cell adhesion assays show a longer binding lifetime of E-selectin (S2Y) to PSGL-1 compared to wildtype protein. CONCLUSIONS: The findings in this study advance our understanding into how the structural makeup of E-selectin allosterically influences its adhesive dynamics.