Structural basis of proton-coupled potassium transport in the KUP family
Igor Tascón, Joana S. Sousa, Robin A. Corey, Deryck J. Mills, David Griwatz, Nadine Aumüller, Vedrana Mikušević, Phillip J. Stansfeld, Janet Vonck, Inga Hänelt
Abstract
Abstract Potassium homeostasis is vital for all organisms, but is challenging in single-celled organisms like bacteria and yeast and immobile organisms like plants that constantly need to adapt to changing external conditions. KUP transporters facilitate potassium uptake by the co-transport of protons. Here, we uncover the molecular basis for transport in this widely distributed family. We identify the potassium importer KimA from Bacillus subtilis as a member of the KUP family, demonstrate that it functions as a K + /H + symporter and report a 3.7 Å cryo-EM structure of the KimA homodimer in an inward-occluded, trans-inhibited conformation. By introducing point mutations, we identify key residues for potassium and proton binding, which are conserved among other KUP proteins.