FIG. 4.

(A) Stereo view of the location of escape mutations on the three-dimensional structure of N2 (A/Tokyo/67) NA (39). The color coding is the same as in Fig. 3. Sialic acid in the active site is shown as a space-filling model. (B) Comparison of crystal structures of NC41 Fab-N9 NA (left) and Mem5 Fab complexed with Mem/98 NA as solved by molecular replacement at 3.5 Å by using Tokyo/67 NA and the NC41 Fv domain (37) as starting models (right). The NA (green) is in the same orientation in both complexes. The antibody heavy chains are red, and light chains are blue.