A positive electron density feature, most likely a low-occupancy water molecule (corresponding to Wat752 in the apo mAChE crystal structure), was found close to the oxime-pyridinium ring (Figures 3A and 3C).
Interestingly, in contrast to HI-6sarinnonaged-mAChE, Asp74 adopts the side-chain conformation found in the apo mAChE and two low-occupancy water molecules (Wat626 and Wat628) seem to bridge the interaction between K027 and Asp74.
Interestingly, some partial-occupancy water molecules are still present and likely co-occur with the major conformations.
Consistent with this mechanism, the secondary conformation of the 79 83 loop is accompanied by an ordered, partial-occupancy water molecule.
While occupancy-water volume slopes for C. guttipennis and H. pulchella were significantly greater than zero, they were lower than the slopes for mosquitoes, which agrees with our prediction that these species would respond less strongly to changes in water volume.
Notably, the relative populations of the two glycerol molecules match the relative number and occupancy of water sites.
We observe partial direct coordination of the side chain carboxylate in D139E with Fe(II); thus, the occupancy of water 2 is reduced similarly.
The average occupancy of water molecules that meet all the three criteria is significantly increased from 0.1% in conformation I to 4.6% in conformation II (Table 2).
Interestingly, the occupancy of water molecules that can be potentially activated before and after disruption of the hydrogen bond is 0.9%and4.3%3%, respectively, which is consistent with the observations of intact covalent-orlistat.
(E ) Scatter plot showing the anti-correlation between the B -factor of explicit solvent molecules in the re-refined single-structure and the relative occupancy of water molecules at that same position (within 0.5-Å distance) in the ensemble model.
As shown in Table 2, the occupancy of water molecules that can strongly hydrogen bond with His is increased from an average of 11% in conformation I to 40% in conformation II (p = 0.051).
