背景回顾：The PIN-FORMED (PIN) protein family of auxin transporters mediates the polar auxin transport and plays crucial roles in plant growth and development. 

主要发现：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. 

结果1-PIN3同源二聚体：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. 

结果2-PIN3参与生长素极性转运机制：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. 

结论：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. 

 摘 要 

生长素运输载体PIN蛋白家族介导了生长素的极性转运，在植物的生长和发育中发挥重要作用。本文中，作者利用冷冻电镜解析了拟南芥AtPIN3蛋白（无配体状态）及其与底物IAA结合状态以及与NPA结合状态下的复合物高分辨率结构。AtPIN3存在同源二聚体，其支架蛋白域中的跨膜螺旋1/2/7参与二聚化。二聚化的AtPIN3蛋白在二聚体界面形成一个面向胞外的腔，每个亚基都是面朝内的构象。结构、功能以及计算模拟显示，揭示了PIN3蛋白上识别IAA和NPA的结构基础，并阐明了NPA抑制PIN蛋白介导的生长素转运的分子机制。AtPIN3蛋白的结构支持生长素运输的“电梯”式模型，负责运输的蛋白域经历上下的刚体运动，而二聚化的支架蛋白域则保持静态。

 郭江涛