GA inhibits cell fusion induced by all three classes of fusion proteins. (A) In the two top panels, typical images used to visualize the extent of fusion in the absence (control, left) and presence of GA (right) are shown. Fused cells (light blue, due to mixing of the green calcein in effector cells and dark blue CMAC in target cells) are marked by arrows in the control. Cells did not fuse in the presence of 10 µM GA. The extent of fusion is quantitated in the bar graph. The experiments used EBOV GP as the fusion protein. (n = 3). For all bars of experiments using cell-cell fusion, means ± SEM are shown. (B) Extent of cell-cell fusion induced by fusion proteins from three classes of viral fusion proteins. The proteins for class I are: ZIKV (Zika E), HIV Env, EBOV (Ebola GP), IAV (Influenza HA); for class II: SFV (Semliki forest virus) E1/E2, VEEV (Venezuelan Equine Encephalitis Virus) E; for class III: VSV (Vesicular Stomatitis Virus) G, EBV (Epstein Barr Virus) gB. Effector cells were transfected (except for HIV Env which was stably expressed in a cell line) with the indicated viral proteins. Each was bound and allowed to fuse with target cells. The reduction in fusion caused by adding 10 µM GA is shown as low grey bars labeled 10 µM GA. For every fusion protein, the presence of GA abolished fusion. n = 3 for each fusion protein. (C) Effect of two different concentrations of GA with different side chains on cell-cell fusion.