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Figure 3.
Fig. 3. A: Hypothtical hydrogen bonding scheme for the D99N
mutant with theNH2 group of Asn-99 hydrogen bonding to His-
48 and Tyr-52. B The alternateconformationofthe Asn-99 side
chain with the NH group pointing away from the His-48 nd hy-
drogen bonding to Tyr-73 and the structural water-3 molecule. The
hydroxyl groups of Tyr-52 nd Tyr-73 have switched orientation
from A to B to accommodatethe hydrogen bonding. Notice hat
the hydrogen bonding pattern of thestructural water molecule in
A and B is different from each other and the WT lthough the
structural water is 4-coordinated in all3 cases. C: The hydrogen
bonding scheme in the X-ray structure of themutant D99N. The
structural water is missing andthe mino roup Asn-99 is
directly hydrogen bonded to thecarbonl group of Ala-1.
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