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Figure 1.
Fig. 1. Crystal structure of Viet04 HA and comparison with 1918
human H1, duck H5, and 1968 human H3 HAs. (A) Overview of the
Viet04 trimer, represented as a ribbon diagram. For clarity,
each monomer has been colored differently. Carbohydrates
observed in the electron-density maps are colored orange, and
all the asparagines that make up a glycosylation site are
labeled. Only Glu20, Glu289, and Phe^154 are not labeled, as
these are on the back of the molecule. The location of the
receptor binding, cleavage, and basic patch sites are
highlighted only on one monomer. All the figures were generated
and rendered with the use of MacPymol (66). (B) Structural
comparison of the Viet04 monomer (olive) with duck H5 (orange)
and 1918 H1 (red) HAs. Structures were first superimposed on the
HA2 domain of Viet04 through the following residues: Viet04,
Gly1 to Pro160; 1918 H1 (PDB: 1rd8), Gly1 to Pro160;
H3(PDB:2hmg), Gly1 to Pro160; H5 (PDB: 1jsm [PDB]
), Gly1 to Pro160. Orientation of the overlay approximates to
the blue monomer in (A). (C) Superimposition of the two long
 -helices of HA2
for 1918 H1 (PDB: 1rd8), avian H5 (PDB: 1jsm [PDB]
), human H3 (PDB: 2hmg [PDB]
), and Viet04 reveal that the extended interhelical loop of
Viet04 is more similar to the 1918 H1 than to the existing avian
H5 structure. The side chain of Phe^63 is illustrated as an
example of the close proximity of the two structures.
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