The PIN-FORMED (PIN) protein family of auxin transporters mediates the polar auxin transport and plays crucial roles in plant growth and development^1,2. Here we present cryo-EM structures of PIN3 from Arabidopsis thaliana (AtPIN3) in the apo state and in complex with its substrate indole-3-acetic acid (IAA) and the inhibitor N-1-naphthylphthalamic acid (NPA) at 2.6–3.0 Å resolution. AtPIN3 exists as a homodimer, with the transmembrane helices (TMs) 1, 2, and 7 in the scaffold domain involved in dimerization. The dimeric AtPIN3 forms a large, joint extracellular-facing cavity at the dimer interface while each subunit adopts an inward-facing conformation. The structural and functional analyses, along with computational studies, reveal the structural basis for the recognition of IAA and NPA and elucidate the molecular mechanism of NPA inhibition on the PIN-mediated auxin transport. The AtPIN3 structures support an elevator-like model for the transport of auxin, whereby the transport domains undergo up-down rigid-body motions and the dimerized scaffold domains remain static.

生长素转运蛋白的 PIN-FORMED (PIN) 蛋白家族介导极性生长素转运，在植物生长发育中起着至关重要的作用^1,2。在这里，我们展示了来自拟南芥(AtPIN3) 的 PIN3 在 apo 状态下的低温电子显微镜结构，并与其底物吲哚-3-乙酸 (IAA) 和抑制剂N形成复合物-1-萘基邻苯二甲酸 (NPA)，分辨率为 2.6–3.0 Å。AtPIN3 作为同型二聚体存在，支架结构域中的跨膜螺旋 (TM) 1、2 和 7 参与二聚化。二聚体 AtPIN3 在二聚体界面处形成一个大的、联合的面向细胞外的空腔，而每个亚基都采用面向内的构象。结构和功能分析以及计算研究揭示了识别 IAA 和 NPA 的结构基础，并阐明了 NPA 抑制 PIN 介导的生长素转运的分子机制。AtPIN3 结构支持类似电梯的生长素运输模型，其中运输域进行上下刚体运动，二聚支架域保持静止。