National Engineering Research Center for Non-Food Biorefinery, Guangxi Academy of Sciences, Nanning, China.
PLoS One. 2011;6(9):e24264. doi: 10.1371/journal.pone.0024264. Epub 2011 Sep 13.
The plant SLAC1 is a slow anion channel in the membrane of stomatal guard cells, which controls the turgor pressure in the aperture-defining guard cells, thereby regulating the exchange of water vapour and photosynthetic gases in response to environmental signals such as drought, high levels of carbon dioxide, and bacterial invasion. Recent study demonstrated that bicarbonate is a small-molecule activator of SLAC1. Higher CO(2) and HCO(3)(-) concentration activates S-type anion channel currents in wild-type Arabidopsis guard cells. Based on the SLAC1 structure a theoretical model is derived to illustrate the activation of bicarbonate to SLAC1 channel. Meanwhile a possible CO(2) conducting and concentrating mechanism of the SLAC1 is proposed.
The homology structure of Arabidopsis thaliana SLAC1 (AtSLAC1) provides the structural basis for study of the conducting and concentrating mechanism of carbon dioxide in SLAC1 channels. The pK(a) values of ionizable amino acid side chains in AtSLAC1 are calculated using software PROPKA3.0, and the concentration of CO(2) and anion HCO(3)(-) are computed based on the chemical equilibrium theory.
The AtSLAC1 is modeled as a five-region channel with different pH values. The top and bottom layers of channel are the alkaline residue-dominated regions, and in the middle of channel there is the acidic region surrounding acidic residues His332. The CO(2) concentration is enhanced around 10(4) times by the pH difference between these regions, and CO(2) is stored in the hydrophobic region, which is a CO(2) pool. The pH driven CO(2) conduction from outside to inside balances the back electromotive force and maintain the influx of anions (e.g. Cl(-) and NO(3)(-)) from inside to outside. SLAC1 may be a pathway providing CO(2) for photosynthesis in the guard cells.
植物 SLAC1 是保卫细胞细胞膜中的一种缓慢阴离子通道，它控制着决定孔径的保卫细胞的膨压，从而调节水蒸气和光合作用气体的交换，以响应环境信号，如干旱、高浓度二氧化碳和细菌入侵。最近的研究表明，碳酸氢盐是 SLAC1 的小分子激活剂。较高的 CO(2)和 HCO(3)(-)浓度会激活野生型拟南芥保卫细胞中的 S 型阴离子通道电流。基于 SLAC1 的结构，提出了一个理论模型来解释碳酸氢盐对 SLAC1 通道的激活。同时，提出了 SLAC1 中 CO(2)传导和浓缩的可能机制。
拟南芥 SLAC1（AtSLAC1）的同源结构为研究 SLAC1 通道中 CO(2)的传导和浓缩机制提供了结构基础。使用软件 PROPKA3.0 计算 AtSLAC1 中可离子化氨基酸侧链的 pK(a)值，并根据化学平衡理论计算 CO(2)和阴离子 HCO(3)(-)的浓度。
将 AtSLAC1 建模为具有不同 pH 值的五区域通道。通道的顶部和底部层是碱性残基主导的区域，在通道的中间有一个环绕酸性残基 His332 的酸性区域。这些区域之间的 pH 值差异将 CO(2)的浓度增强了约 10(4)倍，并且 CO(2)储存在疏水区，形成一个 CO(2)池。pH 值驱动的 CO(2)从外向内传导平衡了反向电动势，并维持阴离子（如 Cl(-)和 NO(3)(-)）从内向外的流入。SLAC1 可能是保卫细胞中光合作用提供 CO(2)的途径。
