Interaction of VAP-1 with the cyclic peptide CARLSLSWRGLTLCPSK (residues 283-297) of Siglec-9. The 3-dimensional structure of VAP-1 (green represents monomer A; and blue, monomer B) with the peptide (pink) derived from Siglec-9 docked into the active site of the monomer B. The close-up view shows that the docked peptide fits well into the active site of VAP-1. Arg284 and Arg290 in the docked peptide are labeled, and Arg284 is covalently bound to topaquinone (TPQ; purple), which is in the active conformation. The figure was created with PYMOL Molecular Graphics System (DeLano Scientific).