Fig. 2: Monte Carlo model relating HA orientation with occlusion of stem antibody binding.

a Structures of pairs of HA-trimers (green and blue), each with three stem Fabs bound in complex (gray), were randomly oriented by rigid rotation relative to each other, and then the resulting complexes were scored for steric clash. The steric clashes were described according to the distance between the base of HA trimers, and the angle between the central axis of HA trimers (orange line). The plot of steric clashes was empirically segmented into three regions: no steric clash (blue), all steric clash (yellow), and conditional steric clash depending upon the interdigitation of Fabs (mixture of blue and yellow). Within the central region of the conditional steric clash, 57% of these configurations are free of steric clash. The two black points in panel a represent the example complexes depicted in panels c and d. b A visualization of the steric clash model system denotes the distance between HA bases, and the angle between central axes of HA trimers. c An example configuration shows parallel HA trimers (angle = 0°) and Fab domains rotated to face each other, but the 190 Å distance between bases avoids steric clash. d An example of HA trimers in the conditional clash region where Fabs interdigitate, avoiding clash in some rotations, but Fabs could easily clash in other rotations of the HA trimer.