Stomata, microscopic pores on plant leaves, regulate gas exchange and water loss by opening or closing in response to environmental cues. Guard cell surrounding each stoma regulate this process by altering their turgor pressure through ion transport, with ionic potassium being the predominant osmotic solutes. 

In Arabidopsis, the outward-rectifying potassium channel GORK drives potassium efflux during stomatal closure. Its bioengineering has demonstrated the potential for enhanced carbon assimilation and water use efficiency.

In a study published online in Nature Communications on Feb. 25, researchers from the Center for Excellence in Molecular Plant Sciences of the Chinese Academy of Sciences and the University of Glasgow, combining structural and functional analyses, revealed the structural basis and unique gating mechanism of Arabidopsis potassium channel GORK.

Researchers first resolved high-resolution structures of GORK channel in closed and pre-open states using cryo-EM. They found that the GORK channel forms a homotetramer with transmembrane pore (PD) and voltage-sensor (VSD) domains, and cytosolic C-linker, cyclic nucleotide-binding homology domain (CNBHD), and ankyrin repeats (ANK) domain. 

Then, researchers found that the interactions center around two coupling sites that functional analysis establish are critical for channel gating. The mutations at Coupling Site I reduced activation energy barriers, accelerated activation, and delayed deactivation, while truncations at Coupling Site II destabilized interactions between the N-terminus and CNBHD, favoring pre-open states. Notably, the channel was also subject to putative, ligand-like interactions within the CNBHD, rendering its gating independence of cyclic nucleotides such as cAMP or cGMP.

These findings demonstrate a multi-step mechanism of semi-independent conformational transitions that underlie channel activity. This study offers promising new sites for optimizing GORK to engineer stomata.