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Figure 2.
Fig. 2. Tertiary structure of the N-domain of STAT-4. (A)
Overall representation of two monomers (green and gray) in the
crystallographic^ dimer, viewed approximately orthogonal to the
molecular twofold^ axis, which is vertical. The ring-shaped
NH[2]-terminal element is colored red in one monomer. (B)
Orthogonal view of one^ of the N-domains shown in (A), depicting
details of the architecture^ of the ring-shaped element. Side
chains that participate in a^ charge-stabilized hydrogen-bond
network are shown in a ball-and-stick representation. The side
chain and backbone carbonyl of buried^ R31 are shown in magenta.
For clarity, the indole ring of the^ invariant residue W4 that
seals off this arrangement on the proximal side is drawn with
thinner bonds. The blue sphere denotes a buried^ water molecule.
Hydrogen bonds are indicated by dotted lines. Oxygen, nitrogen,
and carbon atoms are red, blue, and yellow, respectively. Q3-N
marks the position of the backbone amide group of residue Q3.
The light-red segment of helix  2
highlights its 3[10] helical conformation. Fig. 2 and Fig. 3, B
and C were created^ with the program RIBBONS, version 2.0 (28).
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