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Figure 2.
Figure 2: RBD and ED dimer formation, and the NS1 chain. a,
The RBD and ED of each NS1 molecule separately interact with
their respective domains from the neighbouring NS1 molecules,
related by crystallographic two-fold axes (perpendicular to
plane of the paper indicated the black ovals), resulting in the
formation of a chain of NS1 with alternating RBD and ED dimers.
The two-fold related NS1 molecules are coloured separately in
yellow and green. The residues critical to dsRNA (residues 38
and 41)^16 and CPSF (conserved residues F103, M106 and
GLEWN183-187) binding^14, ^15, ^19 are coloured in blue and red,
respectively. b, Superposition of H5N1 RBD dimer with the H3N2
RBD^6 dimer (in ruby; PDB ID, 1AIL); each protomeric subunit in
the H5N1 RBD dimer is coloured differently in yellow and green.
c, Structural alignment of the H5N1 dimer and H1N1 NS1 ED^7
dimer (in ruby; PDB ID, 2GX9), demonstrating the twisting motion
(curved arrows) of the H5N1 ED monomers, with respect to H1N1
ED, towards their RBDs. Each monomer in the H5N1 NS1 dimer is
coloured as in a. The dimeric interface of the H5N1 NS1 ED
consists of a series of electrostatic interactions: a salt
bridge between K131 and E97, hydrogen-bonding involving the side
chains of T91 and R193, E196 and R200, E152 and the amide group
of L95, as well as a back-bone hydrogen bond between the E96
amide group and the E152 carbonyl group. In contrast, the
dimeric interactions in the H1N1 NS1 ED consists primarily of
strong hydrophobic interactions along the continuous
anti-parallel  -sheet
involving residues L90, V136 and L141 (ref. 7).
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