The rapid (R)-type anion channel plays a central role in controlling stomatal closure in plant guard cells, thus regulating the exchange of water and photosynthetic gas (CO₂) in response to environmental stimuli. The activity of the R- type anion channel is regulated by malate. However, the molecular basis of the R-type anion channel activity remains elusive. Here, we describe the first cryo-EM structure of the R-type anion channel QUAC1 at 3.5 Å resolution in the presence of malate. The structure reveals that the QUAC1 is a symmetrical dimer, forming a single electropositive T-shaped pore for passing anions across the membrane. The transmembrane and cytoplasmic domains are assembled into a twisted bi-layer architecture, with the associated dimeric interfaces nearly perpendicular. Our structural and functional analyses reveal that QUAC1 functions as an inward rectifying anion channel and suggests a mechanism for malate-mediated channel activation. Altogether, our study uncovers the molecular basis for a novel class of anion channels and provides insights into the gating and modulation of the R-type anion channel.

中文翻译：

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保卫细胞中 R 型阴离子通道 QUAC1 活性的分子基础

快速 (R) 型阴离子通道在控制植物保卫细胞的气孔关闭方面起着核心作用，从而调节水和光合气体 (CO ₂) 以响应环境刺激。R-型阴离子通道的活性受苹果酸调节。然而，R 型阴离子通道活性的分子基础仍然难以捉摸。在这里，我们描述了在苹果酸存在下，分辨率为 3.5 Å 的 R 型阴离子通道 QUAC1 的第一个冷冻电镜结构。该结构表明 QUAC1 是一个对称的二聚体，形成一个单一的正电 T 形孔，用于使阴离子穿过膜。跨膜结构域和细胞质结构域组装成扭曲的双层结构，相关的二聚体界面几乎垂直。我们的结构和功能分析表明，QUAC1 作为内向整流阴离子通道发挥作用，并提出了苹果酸介导的通道激活机制。共，