Many of the world's most important food crops such as rice, barley and maize accumulate silicon (Si) to high levels, resulting in better plant growth and crop yields. The first step in Si accumulation is the uptake of silicic acid by the roots, a process mediated by the structurally uncharacterised NIP subfamily of aquaporins, also named metalloid porins. Here, we present the X-ray crystal structure of the archetypal NIP family member from Oryza sativa (OsNIP2;1). The OsNIP2;1 channel is closed in the crystal structure by the cytoplasmic loop D, which is known to regulate channel opening in classical plant aquaporins. The structure further reveals a novel, five-residue extracellular selectivity filter with a large diameter. Unbiased molecular dynamics simulations show a rapid opening of the channel and visualise how silicic acid interacts with the selectivity filter prior to transmembrane diffusion. Our results will enable detailed structure–function studies of metalloid porins, including the basis of their substrate selectivity.

世界上许多最重要的粮食作物，如水稻、大麦和玉米，都会将硅 (Si) 积累到高水平，从而促进植物生长和作物产量。硅积累的第一步是根部吸收硅酸，这一过程由结构上未表征的水通道蛋白 NIP 亚家族介导，也称为准金属孔蛋白。在这里，我们展示了来自Oryza sativa的原型 NIP 家族成员的 X 射线晶体结构(OsNIP2;1)。OsNIP2;1 通道在晶体结构中被细胞质环 D 封闭，已知其调节经典植物水通道蛋白中的通道打开。该结构进一步揭示了一种具有大直径的新型五残基细胞外选择性过滤器。无偏的分子动力学模拟显示了通道的快速打开，并可视化了硅酸在跨膜扩散之前如何与选择性过滤器相互作用。我们的结果将使准金属孔蛋白的详细结构-功能研究成为可能，包括其底物选择性的基础。