Interaction of VAP-1 with Siglec-10 C2-type domain 2. (A) The 3-dimensional structure of VAP-1 (monomer A, yellow; and monomer B, green) with a peptide derived from Siglec-10 CE loop (purple ball-and-stick) docked into the active site of monomer B. Arg293 in the docked peptide is labeled and covalently bound to topaquinone (TPQ), which is in an active conformation. Arm1 and the RGD site in domain A are close to the opening of the active site in VAP-1. At the right, there is a 3-dimensional model of the second Siglec-10 C2 domain shown in an orientation fitting into VAP-1. The amino acids corresponding to the docked ligand are shown as purple ball-and-stick in the Siglec-10 model, and the topaquinone-binding arginine is colored yellow and labeled. (B) Stereo view of Siglec-10 (purple) binding to topaquinone (green) in VAP-1. Grid maps for the amide (blue wires) and carboxylate (red wires) probes are shown at a level of −6 kcal/mol. The asparagine (Asn) in Siglec-10 that corresponds to aspartate in Siglec-11 is labeled. (C) Binding of CHO cells expressing Siglec-10 to CHO cells expressing wild-type VAP-1, the RGD mutant of VAP-1, or mock controls was determined with cell-cell adhesion assay as explained in “Assays with transfectants.” The results are presented as a relative binding ratio ± SEM from 5 separate experiments, each having duplicate wells. *P < .05. (D) Binding of CHO cells expressing Siglec-11 to VAP-1 transfectants. (E) Binding of CHO cells expressing Siglec-G to VAP-1 transfectants. The results of panels D and E are relative binding ratio ± SEM from 2 separate experiments, each having quadruple wells.