Potassium ions (K⁺) are essential for all cells and living organisms. Scientists have long believed that K⁺ merely passes through ion channels and transporters, rather than acting as an extracellular ligand or molecular “switch.” Indeed, there had been no clear evidence that K⁺ functions as a ligand for membrane proteins in animals or plants—until now.
“Unexpectedly, we made this discovery serendipitously while testing the effect of aspartic acid, with K⁺ added as a counter cation, on Alka, an ion channel located in the brain of Drosophila melanogaster,” said the author. “The compound was effective. At first, we thought the effect was due to aspartic acid, but we ultimately realized that it was caused by K⁺, meaning that Alka functions as a membrane receptor that detects extracellular K⁺ as a ligand.”
Ion channel currents in Alka-expressing cells changed significantly in response to K⁺ levels. The researchers combined electrophysiological analysis with AlphaFold3, an AI-based protein structure prediction tool. This allowed them to identify the K⁺-binding site in Alka. This site creates a chemical environment favorable for K⁺, similar to that found in aqueous solution or in the well-known selectivity filter of K⁺ channels.
