FIG 5.

Crystal structure of the H15N9 shWA79 HA in complex with an avian receptor analog. (A) Electron density maps (2Fo − Fc; top) and unbiased 2Fo-Fc electron density map (bottom) of avian receptor analog 3′-SLN in the crystal structure of the H15N9 shWA79 HA contoured at a 1σ level. The glycan structure of the 3′-SLN analog is represented above. Abbreviations: Sia, sialic acid; Gal, galactose; GlcNAc, N-acetylglucosamine. (B) Representation of the interactions between 3′-SLN and the H15 HA RBS. The RBS conserved structural elements are labeled and shown as cartoons. Selected residues and the receptor analog are labeled and shown as sticks. (C) The avian analog 3′-SLN in crystal structures with H10 and H15 HAs adopts a similar trans conformation, but in the H7 3′-SLN complex, it binds in a cis conformation (with regard to the C-1_Sia–C-2_Sia–O–C-3_Gal bond). The H7 HA contains Leu at position 226, while the H10 and H15 HAs have Gln. The superposition was performed on the sialic acid of the sialoside.