Figure 1.

Selectin conformational changes regulated by an interdomain hinge. (A) X-ray structures of the lectin and EGF domains of P-selectin with a closed (left; PDB 1G1Q) and open angle (right; PDB 1G1S; Somers et al., 2000). The golden sphere at the top of the lectin domain represents a Ca²⁺ ion that is coordinated as part of the ligand-binding site. (B) X-ray (left) and MD-simulated (right) structures of the lectin and EGF domains of L-selectin with a closed (left) and open angle (right). The respective open- and closed-angle structures of P- and L-selectin align well. The boxed areas (left) highlight the putative hinge regions that are magnified in the insets. A hydrogen bond (dotted line) connects Tyr37 with Asn138, but not with Gly138. (C) RMSD between the corresponding backbone atoms from residues 121–156 (the EGF domain) of the simulated L-selectin structure and the crystal structures of closed-angle L-selectin (blue curve) or open-angle P-selectin (red curve) as a function of simulation time. The lectin domains were aligned by minimizing the RMSD between the backbone atoms from residues 1–120.