Department of Applied Plant Sciences, Institute of Botany, Darmstadt University of Technology, D-64287 Darmstadt, Germany.
J Biol Chem. 2010 Oct 8;285(41):31253-60. doi: 10.1074/jbc.M110.115881. Epub 2010 Jul 25.
Heterologous expression in yeast cells revealed that NtAQP1, a member of the so-called PIP1 aquaporin subfamily, did not display increased water transport activity in comparison with controls. Instead, an increased CO(2)-triggered intracellular acidification was observed. NtPIP2;1, which belongs to the PIP2 subfamily of plant aquaporins, behaved as a true aquaporin but lacked a CO(2)-related function. Results from split YFP experiments, protein chromatography, and gel electrophoresis indicated that the proteins form heterotetramers when coexpressed in yeast. Tetramer composition had effects on transport activity as demonstrated by analysis of artificial heterotetramers with a defined proportion of NtAQP1 to NtPIP2;1. A single NtPIP2;1 aquaporin in a tetramer was sufficient to significantly increase the water permeability of the respective yeast cells. With regard to CO(2)-triggered intracellular acidification, a cooperative effect was observed, where maximum rates were measured when the tetramer consisted of NtAQP1 aquaporins only. The results confirm the model of an aquaporin monomer as a functional unit for water transport and suggest that, for CO(2)-related transport processes, a structure built up by the tetramer is the basis of this function.
酵母细胞中的异源表达表明，NtAQP1 是所谓的 PIP1 水通道蛋白亚家族的成员，与对照相比，其水运输活性没有增加。相反，观察到 CO(2)触发的细胞内酸化增加。属于植物水通道蛋白 PIP2 亚家族的 NtPIP2;1 表现为真正的水通道蛋白，但缺乏与 CO(2)相关的功能。来自分裂 YFP 实验、蛋白质层析和凝胶电泳的结果表明，这些蛋白质在酵母中共表达时形成异四聚体。四聚体组成对转运活性有影响，这可以通过分析具有特定 NtAQP1 与 NtPIP2;1 比例的人工异四聚体来证明。四聚体中的单个 NtPIP2;1 水通道足以显著增加各自酵母细胞的水通透性。关于 CO(2)触发的细胞内酸化，观察到协同作用，当四聚体仅由 NtAQP1 水通道蛋白组成时，测量到最大速率。结果证实了水通道蛋白单体作为水运输功能单元的模型，并表明对于与 CO(2)相关的运输过程，由四聚体构建的结构是该功能的基础。
