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. 2014 Aug;88(16):9197–9207. doi: 10.1128/JVI.00805-14

FIG 4.

FIG 4

Influenza virus NA second sialic acid binding site. (A) Sequence alignment of the key residues of the influenza virus A NA second sialic acid binding site. All the N1 to N9 NA sequences in the NCBI database are included. The image was created with the WebLogo program (http://weblogo.berkeley.edu/). The overall height of the stack indicates the sequence conservation at that position, while the height of the symbols within the stack indicates the relative frequency of each amino acid at that position. Amino acids that interact with sialic acid are marked with a red star. (B) Structural analysis of the second binding site in N6 (PDB ID 1W20), N9 (PDB ID 1MWE), N2-Tyr406Asp (PDB ID 4H53), and N5. Ser367, Ser370, Ser372, and Asn400 hydrogen bond with Neu5Ac, and Trp403 forms hydrophobic interactions with the Neu5Ac N-acetyl group.