Fig 1.

Crystal structure of the N3 tetramer and analysis of its active site. (A) N3 tetramer in schematic representation, viewed from above the viral surface. (B) Molecular surface of the active site of N3 (yellow); N3 has no 150-cavity. (C) Molecular surface of the active site of H5N1 N1 (red) (PDB ID 2HTY); typical group 1 N1 has a 150-cavity. (D) The covalent complex formed between 3-fluoro-Neu5Ac and N3 Tyr406. The lack of density for the C-2 fluoride leaving group indicates that it has departed, allowing for the formation of the Tyr406-inhibitor covalent bond. (E) Laninamivir bound to the N3 active site with a typical binding mode. (F) Molecular surface of the active site of N2 (blue) (PDB ID 2BAT); group 2 N2 also has no 150-cavity.