Institut des Sciences de Vie, Université Catholique de Louvain, Croix du Sud, 4-L7.07.14, 1348 Louvain-la-Neuve, Belgium.
Biochem J. 2012 Jul 1;445(1):101-11. doi: 10.1042/BJ20111704.
AQPs (aquaporins) are conserved in all kingdoms of life and facilitate the rapid diffusion of water and/or other small solutes across cell membranes. Among the different plant AQPs, PIPs (plasma membrane intrinsic proteins), which fall into two phylogenetic groups, PIP1 and PIP2, play key roles in plant water transport processes. PIPs form tetramers in which each monomer acts as a functional channel. The intermolecular interactions that stabilize PIP oligomer complexes and are responsible for the resistance of PIP dimers to denaturating conditions are not well characterized. In the present study, we identified a highly conserved cysteine residue in loop A of PIP1 and PIP2 proteins and demonstrated by mutagenesis that it is involved in the formation of a disulfide bond between two monomers. Although this cysteine seems not to be involved in regulation of trafficking to the plasma membrane, activity, substrate selectivity or oxidative gating of ZmPIP1s (Zm is Zea mays), ZmPIP2s and hetero-oligomers, it increases oligomer stability under denaturating conditions. In addition, when PIP1 and PIP2 are co-expressed, the loop A cysteine of ZmPIP1;2, but not that of ZmPIP2;5, is involved in the mercury sensitivity of the channels.
水通道蛋白（AQPs）存在于所有生命领域，促进水和/或其他小分子溶质在细胞膜上的快速扩散。在不同的植物水通道蛋白中，质膜内在蛋白（PIPs）分为两个进化群，PIP1 和 PIP2，在植物水分运输过程中发挥关键作用。PIPs 形成四聚体，每个单体作为一个功能通道。稳定 PIP 寡聚体复合物的分子间相互作用以及导致 PIP 二聚体对变性条件具有抗性的原因尚未得到很好的表征。在本研究中，我们鉴定了 PIP1 和 PIP2 蛋白中 A 环的一个高度保守的半胱氨酸残基，并通过突变证明它参与了两个单体之间二硫键的形成。尽管这个半胱氨酸似乎不参与质膜运输、活性、底物选择性或 ZmPIP1s（Zm 是 Zea mays）、ZmPIP2s 和异源寡聚体的氧化门控的调节，但它在变性条件下增加寡聚体的稳定性。此外，当 PIP1 和 PIP2 共表达时，ZmPIP1;2 的 A 环半胱氨酸，但不是 ZmPIP2;5 的 A 环半胱氨酸，参与了通道对汞的敏感性。
