Fig. 3.

Structural titration of GLIC channels. Abundance of GLIC channel conformations as a function of HS-AFM movie frame acquisition number or time. During HS-AFM operation, the pH in the fluid chamber was gradually exchanged from pH 3.4 to pH 7.5 and back to pH 3.4. At the beginning and end of the movie, under active/desensitized-state conditions at pH 3.4, the very similar class 3 and class 2 molecules are most abundant. This structure depicts the ECDs as a flower-shaped pentamer surrounding a central cavity. In the middle of the movie, under closed-state conditions at pH 7.5, class 1 and class 4 molecules dominate, both revealing narrowed ECDs. An asymmetric but well resolved class 5 exists throughout the experiment, but peaks to almost 0.3 upon reexposure to low activating pH. OR, frame number or time, given that the images were acquired at 1 frame per second.