Biophysical characteristics of influenza B HA antigenic sites. (a) Rates of change at individual residues in influenza B HA are shown from the top (T) and viewed along the left (L) and right (R) sides of the monomer. Note that structures marked T and L in panel a are identical to the structures marked “abs” in the rightmost section of Figure 1a, Approximate positions of antigenic sites BA, BB1, BB2, BC, BC, BD, and BE (see Table 2) are indicated with white labels. Color-coding of surface residues is as described in Figure 1b. The most rapidly changing residues in H1 HA (75th percentile and above; red and orange in panel a) were color-coded according to the average pairwise change in NCI values for ∆∆ASA
(tot, panel b), ∆∆ASA
(np, panel c), ∆∆ASA
(pol, panel d), or ∆Q (ch, panel e). Color scheme for panels b-e as in Figure 2f. Structure files used to generate panels a-e, viewable using PyMol, are available on line (Additional files 12, 13, 14, 15 and 16).