Figure 6: 3E1 inhibits low-pH-induced HA conformational change.

(a) Location of the residues forming the 3E1 epitope in the pre-fusion-state monomeric HA (left panel; PDB code: 3LZG) and post-fusion-state monomeric HA (right panel; PDB codes: 1QU1 and 2KXA). The residues of the epitope are shown as red spheres. (b) Protease sensitivity assay of HA in the presence of 3E1 mAb. Exposure of HA to low pH converts the HA to the protease-susceptible, post-fusion state (lanes 3, 7). Treatment of HA with 3E1 mAb before low-pH treatment, but not the control mAb, blocks the pH-induced conformational change, retaining HA in the protease-resistant, pre-fusion state (lanes 4, 8). Data represent a representative experiment from three independent experiments. (c) 3E1 mAb blocks trypsin-activated, low pH-triggered, HA-mediated cell–cell fusion. HEK-293 T cells were transfected with full-length WA11 HA and treated with trypsin, and then 3E1 or control mAb was added followed by low-pH treatment. Treatment of 3E1 mAb could inhibit the formation of syncytium (upper panel), while the control mAb could not (middle panel). Scale bar represents 20 μm. Data represent a representative experiment from three independent experiments.