Saparov Sapar M, Pohl Peter
Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Strasse 10, 13125 Berlin, Germany.
Proc Natl Acad Sci U S A. 2004 Apr 6;101(14):4805-9. doi: 10.1073/pnas.0308309101. Epub 2004 Mar 19.
Water molecules are constrained to move with K+ ions through the narrow part of the Streptomyces lividans K+ channel because of the single-file nature of transport. In the presence of an osmotic gradient, a water molecule requires <10 ps to cross the purified protein reconstituted into planar bilayers. Rinsing K+ out of the channel, water may be 1,000 times faster than the fastest experimentally observed K+ ion and 20 times faster than the one-dimensional bulk diffusion of water. Both the anomalously high water mobility and its inhibition observed at high K+ concentrations are consistent with the view that liquid-vapor oscillations occur because of geometrical confinements of water in the selectivity filter. These oscillations, where the chain of molecules imbedded in the channel (the "liquid") cooperatively exits the channel, leaving behind a near vacuum (the "vapor"), thus far have only been discovered in hydrophobic nanopores by molecular dynamics simulations [Hummer, G., Rasaiah, J. C. & Noworyta, J. P. (2001) Nature 414, 188-190; and Beckstein, O. & Sansom, M. S. P. (2003) Proc. Natl. Acad. Sci. USA 100, 7063-7068].
由于运输的单分子排列特性，水分子在链霉菌钾离子通道的狭窄部分受到限制，只能与钾离子一起移动。在存在渗透梯度的情况下，一个水分子穿过重组到平面双层中的纯化蛋白质所需时间小于10皮秒。将钾离子从通道中冲洗出去后，水的移动速度可能比实验观测到的最快钾离子快1000倍，比水的一维体扩散快20倍。水的异常高迁移率及其在高钾离子浓度下受到的抑制，都与这样一种观点一致，即由于水在选择性过滤器中的几何限制，会发生液-气振荡。到目前为止，这种分子链嵌入通道（“液体”）协同离开通道，留下近乎真空（“蒸汽”）的振荡，仅在通过分子动力学模拟的疏水纳米孔中被发现[Hummer, G., Rasaiah, J. C. & Noworyta, J. P. (2001) Nature 414, 188 - 190; 以及Beckstein, O. & Sansom, M. S. P. (2003) Proc. Natl. Acad. Sci. USA 100, 7063 - 7068]。
