State Key Laboratory of Medicinal Chemical Biology and College of Life Sciences, Nankai University, Tianjin 300350, China.
Key Laboratory of Plant Molecular Physiology, Institute of Botany, Innovation Academy for Seed Design, Chinese Academy of Sciences, Beijing 100093, China; College of Life Science, University of Chinese Academy of Sciences, Beijing 100049, China.
Cell Rep. 2024 Sep 24;43(9):114731. doi: 10.1016/j.celrep.2024.114731. Epub 2024 Sep 12.
The Arabidopsis thaliana aluminum-activated malate transporter 9 (AtALMT9) functions as a vacuolar chloride channel that regulates the stomatal aperture. Here, we present the cryoelectron microscopy (cryo-EM) structures of AtALMT9 in three distinct states. AtALMT9 forms a dimer, and the pore is lined with four positively charged rings. The apo-AtALMT9 state shows a putative endogenous citrate obstructing the pore, where two W120 constriction residues enclose a gate with a pore radius of approximately 1.8 Å, representing an open state. Interestingly, channel closure is solely controlled by W120. Compared to wild-type plants, the W120A mutant exhibits more sensitivity to drought stress and is unable to restore the visual phenotype on leaves upon water recovery, reflecting persistent stomatal opening. Furthermore, notable variations are noted in channel gating and substrate recognition of Glycine max ALMT12, AtALMT9, and AtALMT1. In summary, our investigation enhances comprehension of the interplay between structure and function within the ALMT family.
拟南芥铝激活苹果酸转运蛋白 9（AtALMT9）作为液泡氯离子通道发挥作用，调节气孔开度。在这里，我们呈现了三种不同状态下的 AtALMT9 的冷冻电镜（cryo-EM）结构。AtALMT9 形成二聚体，孔道由四个带正电荷的环排列而成。apo-AtALMT9 状态显示出一种内源性柠檬酸可能阻塞孔道的情况，其中两个 W120 收缩残基包围着一个带有约 1.8Å 孔径的门，代表开放状态。有趣的是，通道关闭仅由 W120 控制。与野生型植物相比，W120A 突变体对干旱胁迫更敏感，并且在水恢复后无法恢复叶片的视觉表型，反映出持续的气孔开度。此外，在 Glycine max ALMT12、AtALMT9 和 AtALMT1 的通道门控和底物识别方面也观察到明显的差异。总之，我们的研究增进了对 ALMT 家族结构与功能相互作用的理解。
