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Figure 7.
FIG. 7. Interactions between the thiodisaccharide and the
+1 and -1 binding sites in human ERManI. Shown is a schematic
diagram (left panel) of the interactions between the
thiodisaccharide and ERManI in the -1 and +1 subsites,
demonstrating hydrogen bonding interactions (green dotted
lines), direct coordination of the enzyme-associated Ca^2+ ion
(blue dotted lines), hydrophobic stacking of Phe^659 with the
C-4-C-5-C-6 region of the -1 residue (black dotted lines), and
proposed acid-catalyzed through-water (W8) protonation of the
glycosidic oxygen (sulfur in the thiodisaccharide) and the
base-catalyzed (Glu599) attack by the water nucleophile (W5)
(red dotted lines). Residue numbering of amino acid side chains
in the respective subsites is indicated. The stereo view (center
and right) illustrates a stick diagram of the interaction
between the thiodisaccharide residues in the -1 and +1 subsites
relative to the residues examined by mutagenesis here.
Coordination to the Ca^2+ ion (blue dotted lines), and the
proposed nucleophile trajectory and acid protonation of the
glycosidic oxygen (red dotted lines) are indicated. The small
red and green space fill structures representing the water
molecules and carbonyl oxygen and O-  of Thr688 that
coordinate the Ca^2+ ion are as described in the legend to Fig.
2. The green dotted lines indicate hydrogen bonds between the
respective residues.
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