Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, Japan.
Pharmaceuticals and Medical Devices Agency, Tokyo, Japan.
Nat Struct Mol Biol. 2018 Sep;25(9):797-804. doi: 10.1038/s41594-018-0109-6. Epub 2018 Aug 20.
Maintenance of cell volume against osmotic change is crucial for proper cell functions. Leucine-rich repeat-containing 8 proteins are anion-selective channels that extrude anions to decrease the cell volume on cellular swelling. Here, we present the structure of human leucine-rich repeat-containing 8A, determined by single-particle cryo-electron microscopy. The structure shows a hexameric assembly, and the transmembrane region features a topology similar to gap junction channels. The LRR region, with 15 leucine-rich repeats, forms a long, twisted arc. The channel pore is located along the central axis and constricted on the extracellular side, where highly conserved polar and charged residues at the tip of the extracellular helix contribute to permeability to anions and other osmolytes. Two structural populations were identified, corresponding to compact and relaxed conformations. Comparing the two conformations suggests that the LRR region is flexible and mobile, with rigid-body motions, which might be implicated in structural transitions on pore opening.
维持细胞体积对抗渗透变化对于正常的细胞功能至关重要。富含亮氨酸重复序列的 8 蛋白是阴离子选择性通道，可在细胞肿胀时排出阴离子以减小细胞体积。本文通过单颗粒冷冻电镜确定了人富含亮氨酸重复序列 8A 的结构。结构显示出六聚体组装，跨膜区域具有与缝隙连接通道相似的拓扑结构。LRR 区域包含 15 个富含亮氨酸的重复序列，形成一个长而扭曲的弧形。通道孔位于中央轴线上，并在细胞外侧面受限，细胞外螺旋尖端的高度保守极性和带电残基有助于阴离子和其他渗透物的通透性。鉴定出两种结构群体，分别对应于紧凑和放松的构象。比较两种构象表明，LRR 区域是灵活和可移动的，具有刚体运动，这可能与孔开口的结构转变有关。
