AI-guided discovery of a novel ATP/ADP binding domain in plant HAK transporters that regulates K+/Na+ homeostasis
摘要
Maintaining Na+/K+ homeostasis is fundamental for plant environmental adaptation. Using domain classification of plant Na+/K+ transport proteins, and AI-based ligand screening integrated with biochemical characterization, we identified a previously unannotated cytoplasmic domain (CPD) in plant HAKs as a novel ATP/ADP-binding fold. We demonstrate that ATP/ADP binding to the CPD directly couples to the gating of ion transport, a regulatory mechanism previously unknown in this transporter family. Cryo-EM structures of Arabidopsis HAK5 in ADP-bound and ligand-free states, alongside Zea mays HAK4 in an ATP-bound state, revealing a distinctive autoinhibitory mechanism. In the ADP-bound state, the CPD physically obstructs the transmembrane ion pathway. Conversely, the gain-of-function mutant AtHAK5D152A triggers a downward translocation of the CPD to release this inhibition, which is corroborated by the ATP binding conformation of ZmHAK4. Our study defines the structural basis for ATP/ADP- associated gating in plant HAK transporters, providing a novel molecular framework for engineering salt-tolerant crops.
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