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Figure 3.
FIGURE 3. A, glucose bound to the SsGDH active site in the
A-monomer. Coloring is as in Fig. 2B with the mutation T41A
highlighted by orange carbons and the glucose molecule shown
with purple carbons and red oxygens, with both C6-hydroxyl
conformations. Unbiased F[c] -F[c] electron density for the
substrate is shown as green mesh (contoured at 2.25  ).
Hydrogen bonds between the protein and glucose are shown as
broken black lines, and gray broken lines indicate interactions
of 3.5-3.7 Å that are possible hydrogen bonds at the
moment of catalysis. Asp^154 sits below the sugar ring
interacting with the C2- and C3-hydroxyls. B, xylose bound to
the SsGDH active site of monomer A. Coloring is as in A, but the
glucose molecule is shown in the equatorial  -form with purple
carbons and red oxygens, and in the axial (  -form) with
wheat-colored carbons. Unbiased F[c] - F[c] electron density for
the substrate is shown as green mesh (contoured at 2.25 ).
Hydrogen bonds between the protein and -xylose are shown as
broken black lines, and gray broken lines indicate interactions
of <3.5-3.7 Å that are possible hydrogen bonds at the
moment of catalysis. Hydrogen bonds to the -form are not shown,
because most, with the exception of the C1-OH interactions, are
maintained and no new hydrogen bonds are formed in the -form.
C, superposition of glucose (green) and xylose (blue) in the
active site of the A-monomer. The two positions for O6 of
glucose are displayed, as are the two positions of O1 of xylose.
Glu^114 undergoes a conformational change between the glucose
and xylose complex structures; the alternative position for this
residue in the xylose structure is depicted in wheat-colored
carbons.
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