Tania Shaila Shermin, Utsugi Shigeko, Tsuchiya Yoshiyuki, Sasano Shizuka, Katsuhara Maki, Mori Izumi C
Institute of Plant Science and Resources, Okayama University, Kurashiki, Okayama, Japan.
Plant Cell Environ. 2025 Sep;48(9):6835-6846. doi: 10.1111/pce.15635. Epub 2025 Jun 3.
The transport of CO across biomembranes in plant cells is essential for efficient photosynthesis. Some aquaporins capable of CO transport, referred to as 'COOporins', are postulated to play a crucial role in leaf CO diffusion. However, the structural basis of CO permeation through aquaporins remains largely unknown. Here, we show that amino acids in loop C are critical for the CO permeability of Arabidopsis thaliana PIP2 aquaporins. We found that swapping tyrosine and serine in loop C to histidine and phenylalanine, which differ between AtPIP2;1 and AtPIP2;3, altered CO permeability when examined in the Xenopus laevis oocyte heterologous expression system. AlphaFold2 modelling indicated that these substitution induced a conformational shift in the sidechain of arginine in the aromatic/arginine (ar/R) selectivity filter and in lysine at the extracellular mouth of the monomeric pore in PIP2 aquaporins. Our findings demonstrate that distal amino acid substitutions can trigger conformational changes of the ar/R filter in the monomeric pore, modulating CO permeability. Additionally, phylogenetic analysis suggested that aquaporins capable of dual water/CO permeability are ancestral to those that are water-selective and CO-impermeable, and CO-selective and water impermeable.
二氧化碳在植物细胞生物膜上的运输对于高效光合作用至关重要。一些能够运输二氧化碳的水通道蛋白，被称为“二氧化碳通道蛋白”，被认为在叶片二氧化碳扩散中起关键作用。然而，二氧化碳通过水通道蛋白渗透的结构基础仍 largely 未知。在这里，我们表明环 C 中的氨基酸对于拟南芥 PIP2 水通道蛋白的二氧化碳通透性至关重要。我们发现，将环 C 中的酪氨酸和丝氨酸换成组氨酸和苯丙氨酸（AtPIP2;1 和 AtPIP2;3 之间存在差异），在非洲爪蟾卵母细胞异源表达系统中检测时会改变二氧化碳通透性。AlphaFold2 建模表明，这些取代诱导了芳香族/精氨酸（ar/R）选择性过滤器中精氨酸侧链以及 PIP2 水通道蛋白单体孔细胞外口处赖氨酸的构象变化。我们的研究结果表明，远端氨基酸取代可引发单体孔中 ar/R 过滤器的构象变化，调节二氧化碳通透性。此外，系统发育分析表明，具有水/二氧化碳双重通透性的水通道蛋白是水选择性且二氧化碳不渗透以及二氧化碳选择性且水不渗透的水通道蛋白的祖先。
