Structural insights into auxin recognition and efflux by Arabidopsis PIN1 – Nature

Polar auxin transport (PAT) is unique to plants and coordinates their growth and development^1,2. The PIN-FORMED (PIN) auxin transporters with remarkable asymmetrical localizations at the plasma membrane drive PAT^3,4, however, their structures and transport mechanisms remain largely unknown. Here, we report three inward-facing conformation structures of the major member of the PIN family, PIN1 in Arabidopsis thaliana (AtPIN1): (i) in the apo state, (ii) in the natural auxin, indole-3-acetic acid (IAA)-bound state, and (iii) in complex with the PAT inhibitor N-1-naphthylphthalamic acid (NPA). The transmembrane domain of AtPIN1 shares a conserved NhaA-fold⁵. In the substrate-bound structure, IAA is coordinated through both hydrophobic stacking and hydrogen bonding. The inhibitor NPA competes with IAA for the same site of the intracellular pocket with a much higher affinity. These findings facilitate our understanding of the substrate recognition and transport mechanisms of PINs, and set up a framework for future research on the directional auxin movement, one of the most crucial processes underlying plant development.