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Figure 2.
Fig. 2. The dimer interface. (a) Dimerization interface
region with one subunit as a surface representation (hydrophilic
contact residues in light blue and hydrophobic contact residues
in green) and the other subunit as transparent ribbon diagram
colored as in Fig. 1b (β-strands A, B, and E are shown in blue;
strands CC′FGG′ are shown in red; a 3[10] helix is shown in
purple; and loops are shown in gray). Strands are labeled in
white, and contact residues are shown as sticks. (b) Cross
section of the dimer interface illustrating the two symmetrical
intersubunit salt bridges (green lines) between Asp44 and Arg72.
Water molecules (yellow spheres) that mediate a hydrogen bond
network (yellow dotted line) between the Gln34 residues of each
subunit are also shown. Strands are labeled in white and colored
as described above. (c) Proposed orientation of a CHIR-AB1 dimer
on a membrane (gray line). Monomers are colored as in Fig. 1b.
The 2-fold symmetry axis relating the monomers is indicated by a
vertical green dotted arrow on the plane of the page. The
distance between the C-terminus of each ectodomain (45 Å)
and the approximate length of the ectodomain (  vert,
similar 35 Å) is indicated (black dashed lines). The
eight-residue stem region connecting each ectodomain subunit to
the transmembrane region is shown as a broken black bar with a
maximum theoretical length of vert,
similar 30 Å (calculated assuming 3.8 Å per
residue). (d) Molecular surfaces of the two subunits in a
CHIR-AB1 dimer, with colors highlighting the electrostatic
potential calculated with APBS tools.^24 Electrostatic potential
is plotted from − 11.2 kT/e (electronegative; red) to + 11.2
kT/e (electropositive; blue), with white indicating
electroneutrality. The right monomer is related to the left
monomer by a rotation about the indicated axis of vert,
similar 170°. Black arrows point toward contact partner
residues.
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