Structural insights into the transport and gating mechanisms of the plant high-affinity K+ transporter AtHAK5
Abstract
Plant high-affinity K⁺ (HAK) transporters are essential for survival in nutrient-depleted soils. However, the mechanisms governing their energetically costly active transport and stringent regulation have remained structurally elusive. Here, we present high-resolution cryo-EM structures of Arabidopsis thaliana HAK5, revealing a homodimeric assembly characterized by a modified LeuT-fold. A unique topological "knot" within the permeation pathway establishes a selective K⁺ coordination site and coordinates critical residues facilitating proton-coupled symport. Unexpectedly, we discovered a uniquely folded adenine nucleotide-binding domain (NBD) at the cytoplasmic interface. The bound endogenous ADP orients an intracellular loop (ICLgate) to physically plug the intracellular exit of the pore. Crucially, structural analysis of rationally engineered nucleotide-binding mutants reveals a substantial rigid-body rearrangement of the cytoplasmic domain that displaces this plug to open the gate. Validated by in vivo yeast complementation assays, these structural insights unveil a sophisticated autoinhibitory mechanism that directly couples the mechanical gating of ion transport to the cellular energy status. This study provides a definitive structural framework for understanding plant HAK transporters and offers a crucial blueprint for engineering nutrient-efficient crops.
References
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