Homophilic interactions of PECAM-1 IgD1. (A) The IgD1/D1 interface. Interfacial residues defined by PDBsum⁵¹  are shown as sticks, with transparent surfaces and carbons in magenta for PECAM-1 IgD1-D2 molecule 1 or yellow for PECAM-1 IgD1-D2 molecule 2. Glycans at N25 and N57 are shown as sticks with carbon in wheat color. Oxygens and nitrogens are red and blue, respectively. Residues that are important for homophilic binding as identified by previous mutagenesis studies are boxed. (B) Close-up of the IgD1/D1 interface. One of the IgD1 molecules is shown as a transparent surface. The epitope of mAb PECAM-1.3 is highlighted with carbons in green. Waters are red small spheres. Hydrogen bonds are dashed in green. (C) Epitope mapping of mAb PECAM-1.3 bound to a series of overlapping peptides spanning PECAM-1 amino acids 29-50. (D-F) A split view of the IgD1/D1 interface as shown in panel B. The interacting residues are listed in panel F with hydrogen bonds and nonbonded contacts shown in green and orange, respectively. The equivalent residues that differ in mouse PECAM-1 are shown in red. The interfacial residues are also indicated in Figure 2.