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. Author manuscript; available in PMC: 2020 Aug 5.
Published in final edited form as: J Am Chem Soc. 2019 Jul 11;141(29):11481–11488. doi: 10.1021/jacs.9b02196

Figure 5.

Figure 5.

F48 Cδ–Hδpeak shows conformational equilibration between the Inwardopen(blue) and Inwardclosed (red) states of M2(19–49) WT as a function of pH. Top: Only the Inwardopen state is observed at pH 3.4 and 4.3. In the physiologically relevant pH range (5.0–7.5), both conformational states are observed. The peak of the Inwardclosed conformation (red) gains intensity at pH 5.0, reaches a maximum at pH 6.0, and then decreases at higher pH. The data are normalized to the intensity observed at pH 3.4, and sum to slightly less than 100%, possibly due to a third state that is not detected due to chemical exchange or dynamics. Bottom: Fit of peak intensity vs pH for both conformational states. The intensity profile of the Inwardopen conformation (blue) has a U-like shape with a minimum at pH ∼6.0. The channel primarily adopts the Inwardopen conformation at both very low and very high pH.