Visualization of a water-selective pore by electron crystallography in vitreous ice

The water-selective pathway through the aquaporin-1 membrane channel has been visualized by fitting an atomic model to a 3.7-Å resolution three-dimensional density map. This map was determined by analyzing images and electron diffraction patterns of lipid-reconstituted two-dimensional crystals of aquaporin-1 preserved in vitrified buffer in the absence of any additive. The aqueous pathway is characterized by a size-selective pore that is ≈4.0 ± 0.5Å in diameter, spans a length of ≈18Å, and bends by ≈25° as it traverses the bilayer. This narrow pore is connected by wide, funnel-shaped openings at the extracellular and cytoplasmic faces. The size-selective pore is outlined mostly by hydrophobic residues, resulting in a relatively inert pathway conducive to diffusion-limited water flow. The apex of the curved pore is close to the locations of the in-plane pseudo-2-fold symmetry axis that relates the N- and C-terminal halves and the conserved, functionally important N76 and N192 residues.

研究人员通过将原子模型拟合至3.7埃（Å）分辨率的三维密度图，已可视化水通道蛋白-1（aquaporin-1）膜通道的水选择性通路。该密度图通过分析在无任何添加剂的玻璃态缓冲液中保存的、经脂质重构的水通道蛋白-1二维晶体的成像数据与电子衍射图样获得。该水通路以尺寸选择性孔道为特征：其直径约为4.0 ± 0.5埃，孔道跨度约为18埃，在穿越脂质双分子层时发生约25°的弯曲。该狭窄孔道在细胞外侧与细胞质侧分别通过宽阔的漏斗状开口与外界连通。尺寸选择性孔道的内壁主要由疏水残基构成，形成了相对惰性的通路，利于以扩散限制方式进行的水流运动。弯曲孔道的顶点靠近平面内伪二重对称轴的位置，该对称轴关联着蛋白的N端与C端结构域，同时也对应保守且功能至关重要的N76与N192残基的所在位点。