Structural titration of receptor ion channel GLIC gating by HS-AFM

Proc Natl Acad Sci U S A. 2018 Oct 9;115(41):10333-10338. doi: 10.1073/pnas.1805621115. Epub 2018 Sep 4.


Gloeobacter violaceus ligand-gated ion channel (GLIC), a proton-gated, cation-selective channel, is a prokaryotic homolog of the pentameric Cys-loop receptor ligand-gated ion channel family. Despite large changes in ion conductance, small conformational changes were detected in X-ray structures of detergent-solubilized GLIC at pH 4 (active/desensitized state) and pH 7 (closed state). Here, we used high-speed atomic force microscopy (HS-AFM) combined with a buffer exchange system to perform structural titration experiments to visualize GLIC gating at the single-molecule level under native conditions. Reference-free 2D classification revealed channels in multiple conformational states during pH gating. We find changes of protein-protein interactions so far elusive and conformational dynamics much larger than previously assumed. Asymmetric pentamers populate early stages of activation, which provides evidence for an intermediate preactivated state.

Keywords: Cys-loop; GLIC; HS-AFM; conformational change; ion channel.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Cyanobacteria / chemistry
  • Cysteine Loop Ligand-Gated Ion Channel Receptors / chemistry*
  • Cysteine Loop Ligand-Gated Ion Channel Receptors / metabolism
  • Hydrogen-Ion Concentration
  • Ion Channel Gating / physiology
  • Microscopy, Atomic Force / methods*
  • Protein Conformation


  • Bacterial Proteins
  • Cysteine Loop Ligand-Gated Ion Channel Receptors