Figure 1. Schematic of the trimeric influenza virus HA.
The membrane distal globular head domain is shown in red and the membrane proximal stalk domain is shown in blue. Cysteines 52 and 277 - which form a disulfide bond that demarcates head and stalk domain - are shown in yellow. The schematic is based on the H1 HA of A/PR/8/34 (PDB 1RU7 as described in [92]).