FIGURE 4.

Residues at the C terminus of PB2 implicated in host adaptation. a, the PB2 627-NLS domain comprises two independently folded domains, the 627 domain (dark gray) and the NLS domain (light gray), interacting via a polar interface (57). Residues implicated in host adaptation (67) are shown in yellow. b, the crystal structures show electrostatic surface potentials of the human 627 domain with Lys-627 (left) and a point mutant with the avian-like Glu-627 residue (right). Formation of a large basic surface occurs upon host adaptation that is mediated almost universally by an E627K mutation.