PaperRSS文献速递| 高等植物吸收硅的结构基础，OsNIP2;1的射线晶体结构解析

类金属是具有物理和化学性质的介于金属和非金属之间的元素。硅(Si)是地壳中含量最丰富的金属，在许多植物中含量都很高，尤其是禾本科植物(草类)。世界上大多数的主要粮食作物，如水稻、大麦和玉米，都积累了大量的硅，从而产生了对非生物和生物胁迫的抗性，从而改善了植物生长和作物产量。

硅积累的第一步是通过根吸收硅酸(Si)，硅的生物可利用性，这一过程是由水通道蛋白的结构未知的NIP亚家族介导的。

图1 OsNIP2的x射线晶体结构

本文介绍了水稻(Oryza sativa)典型NIP家族成员(OsNIP2;1)的x射线晶体结构。当OsNIP2;1通道在晶体中通过胞内环路D闭合时，无偏分子动力学(MD)模拟显示了亚微秒时间尺度上的一个快速通道打开。MD模拟进一步显示了硅如何与胞外五残基选择性过滤器相互作用，该过滤器为跨膜扩散提供了主要屏障。我们的数据为理解和潜在的操纵一个重要的和有待研究的水通道蛋白亚家族的金属选择性提供了基础。

Metalloids are elements with physical and chemical properties that are intermediate between metals and non-metals. Silicon (Si) is the most abundant metalloid in the Earth's crust and occurs at high levels in many plants, especially those belonging to the Poaceae (grasses). Most of the world's staple food crops such as rice, barley and maize accumulate silicon to high levels, resulting in resistance to abiotic and biotic stresses and consequently better plant growth and crop yields. The first step in silicon accumulation is the uptake of silicic acid (Si), the bioavailable from of silicon, by the roots, a process mediated by the structurally uncharacterised NIP subfamily of aquaporins. Here we present the X-ray crystal structure of the archetypal NIP family member from Oryza sativa (OsNIP2;1). While the OsNIP2;1 channel is closed in the crystal by intracellular loop D, unbiased molecular dynamics (MD) simulations reveal a rapid channel opening on sub-microsecond time scales. MD simulations further show how Si interacts with an extracellular five-residue selectivity filter that provides the main barrier for transmembrane diffusion. Our data provide a foundation for understanding and potential manipulation of metalloid selectivity of an important and understudied aquaporin subfamily.

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