TY - JOUR T1 - Structural basis for Potassium transport by KdpFABC JF - bioRxiv DO - 10.1101/2021.01.09.426067 SP - 2021.01.09.426067 AU - Marie E. Sweet AU - Casper Larsen AU - Xihui Zhang AU - Michael Schlame AU - Bjørn P. Pedersen AU - David L. Stokes Y1 - 2021/01/01 UR - http://biorxiv.org/content/early/2021/01/10/2021.01.09.426067.abstract N2 - KdpFABC is an oligomeric K+ transport complex in prokaryotes that maintains ionic homeostasis under stress conditions. The complex comprises a channel-like subunit (KdpA) from the Superfamily of K+ Transporters and a pump-like subunit (KdpB) from the superfamily of P-type ATPases. Recent structural work has defined the architecture and generated contradictory hypotheses for the transport mechanism. Here, we use substrate analogs to stabilize four key intermediates in the reaction cycle and determine the corresponding structures by cryo-EM. We find that KdpB undergoes conformational changes consistent with other representatives from the P-type superfamily, whereas KdpA, KdpC and KdpF remain static. We observe a series of spherical densities that we assign as K+ or water and which define a pathway for K+ transport. This pathway runs through an intramembrane tunnel in KdpA and delivers ions to sites in the membrane domain of KdpB. Our structures suggest a mechanism where ATP hydrolysis is coupled to K+ transfer between alternative sites in the membrane domain of KdpB, ultimately reaching a low-affinity site where a water-filled pathway allows release of K+ to the cytoplasm.Competing Interest StatementThe authors have declared no competing interest. ER -