Interaction between Siglec-9 and VAP-1 involves both enzyme activity-dependent and independent mechanisms. (A) Binding of CFSE-labeled CHO-Siglec-9 transfectants to CHO cells expressing wild-type VAP-1 (CHO-VAP-1), or the enzymatically inactive VAP-1 (CHO-VAP-1Y471F) and to mock-transfected controls (CHO-mock). Binding is expressed as relative binding (mean ± SD, n = 5). *P < .05. **P < .01. ***P < .001. (B) Fluorescence microscopy images of the binding are shown as indicated. The images were taken with Zeiss Axiovert 200M microscope using LD A-plan 20×/0.30 Ph1 Var1 objective and Hamamatsu 1394 ORCA-B2 camera. The software was AxioVision Version 4.5. (C) Surface plasmon resonance analyses of the cyclic wild-type Siglec-9–like peptide at different concentrations (0-400 μM). (D) An example of surface plasmon resonance analyses with the wild-type and the mutated Siglec-9–like peptides. Three experiments were performed with comparable results. Arg 1 indicates Arg 284; Arg 2, Arg 290; and Pept, wild-type peptide.