Nature Communications (Jun 2024)

Structure and mechanism of the K+/H+ exchanger KefC

  • Ashutosh Gulati,
  • Surabhi Kokane,
  • Annemarie Perez-Boerema,
  • Claudia Alleva,
  • Pascal F. Meier,
  • Rei Matsuoka,
  • David Drew

DOI
https://doi.org/10.1038/s41467-024-49082-7
Journal volume & issue
Vol. 15, no. 1
pp. 1 – 14

Abstract

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Abstract Intracellular potassium (K+) homeostasis is fundamental to cell viability. In addition to channels, K+ levels are maintained by various ion transporters. One major family is the proton-driven K+ efflux transporters, which in gram-negative bacteria is important for detoxification and in plants is critical for efficient photosynthesis and growth. Despite their importance, the structure and molecular basis for K+-selectivity is poorly understood. Here, we report ~3.1 Å resolution cryo-EM structures of the Escherichia coli glutathione (GSH)-gated K+ efflux transporter KefC in complex with AMP, AMP/GSH and an ion-binding variant. KefC forms a homodimer similar to the inward-facing conformation of Na+/H+ antiporter NapA. By structural assignment of a coordinated K+ ion, MD simulations, and SSM-based electrophysiology, we demonstrate how ion-binding in KefC is adapted for binding a dehydrated K+ ion. KefC harbors C-terminal regulator of K+ conductance (RCK) domains, as present in some bacterial K+-ion channels. The domain-swapped helices in the RCK domains bind AMP and GSH and they inhibit transport by directly interacting with the ion-transporter module. Taken together, we propose that KefC is activated by detachment of the RCK domains and that ion selectivity exploits the biophysical properties likewise adapted by K+-ion-channels.