FIG 3.

Additive effect on H-F glycoprotein interaction by combined mutations in CDV F. (A) Homology model of the prefusion CDV F trimer (red). The four critical residues in the cavity F microdomain that dramatically affected membrane fusion when they were changed to polar or charged amino acids are highlighted in green. (B) Syncytium formation assay. Cell-to-cell fusion activity was determined as described in the legend to Fig. 1B. (C) Cell surface assessment of H interaction with cleaved F proteins. CoIPs were performed as described in the legend to Fig. 2A. For clarity, gels were cropped, and the black lines indicate the cropping site. (D) Semiquantitative assessment of F/H avidity of interactions. The strength of F-H interactions was calculated as described in the legend to Fig. 2B. Values are averages of results from at least three independent experiments.