Sequence alignment of PECAM-1 IgD1-D2 across species. The alignment was generated with the ESPript server⁴⁸  and modified manually. Conserved residues are boxed and highlighted in red. Secondary structures were defined by the DSSP program^49,50  based on the crystal structure of PECAM-1. Disulfide linkages, N-linked glycosylation sites, the epitope for mAb PECAM-1.3, and the IgD1-D2 boundary are indicated. The interfacial residues are marked with different shapes, with color codes corresponding to Figures 4 and 5. The F-G bridge region and the swapped G strand are indicated with blue bars.