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Figure 4.
Fig. 4. Swine H9 and human H3 HA binding sites preferring
 2,6
linkages are wider than avian H5 preferring 2,3. The H9
swine (gray), H3 human (green), and H5 avian (white) 226/228
loops are superimposed, showing that the H5 avian 220s loop
(Gln-226/Gly-228) is closer to the opposing 130s loop than the
H9 swine (Leu-226/Gly-228) or H3 human (Leu-226/Ser-228).
Contact between Ala-138 and the lower methyl group of Leu-226
requires a more "open" site. The glycosidic oxygen of sialic
acid (atom colors) is labeled with an asterisk. A water molecule
(red sphere) mediates interactions between the amide group of
Gly-228 and the 8- and 9-OHs of sialic acid in H9 swine and H5
avian HAs. The hydroxyl group of Ser-228 "replaces" the water
molecule to form a hydrogen bond with 9-OH in the H3 human HA.
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