Relative binding footprint of individual within the HA stem epitope.

<p>Surface structure models of hemagglutinin (HA) A(H1N1)pdm09 (PDB structure 3AL4) showing the two domains (HA1 in blue, HA2 in violet) and the key epitope residues of each sdAb. The key epitope residues of human antibody CR6261, defined by X-ray crystallography [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164296#pone.0164296.ref022" target="_blank">22</a>], is indicated with a dotted black line and demonstrates overlapping sdAb epitopes. The epitope footprint of each sdAb is shown in red relative to the HA stem and combines residues identified by deep mutational scanning (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164296#pone.0164296.g005" target="_blank">Fig 5</a>) and rational mutagenesis with naturally occurring subtype specific substitutions (Fig 7). The final panel shows a exploded view of the R1a-B6 epitope with key Gly²⁰, Trp²¹ and Ile⁴⁵ residues shown in red. Helix A and fusion peptide are highlighted in yellow and green respectively.