Biophysical characteristics of influenza H1 HA antigenic sites. (a) Rates of change at individual residues in H1 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 leftmost section of Figure 1a with approximate positions of antigenic sites Ca1, Ca2, Cb, Sa, Sb, and H1C (see Table 2) 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). (f) Color scheme for panels b-e: residues whose absolute rate of change is lower than the 75th percentile, white, residues in the top 25th percentile in terms of absolute amino acid changes but whose change in the value of interest was below the 50th percentile of all residues in HA1, blue; values between 50th and 75th percentile, green; values between 50th and 90th percentile, orange; values above 90th percentile, red. Structure files used to generate panels a-e, viewable using PyMol, are available on line (Additional files 2, 3, 4, 5 and 6).