School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China; Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai 200031, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), 13125 Berlin, Germany.
Cell Rep. 2023 Aug 29;42(8):112926. doi: 10.1016/j.celrep.2023.112926. Epub 2023 Aug 6.
Volume-regulated anion channels (VRACs) are hexamers of LRRC8 proteins that are crucial for cell volume regulation. N termini (NTs) of the obligatory LRRC8A subunit modulate VRACs activation and ion selectivity, but the underlying mechanisms remain poorly understood. Here, we report a 2.8-Å cryo-electron microscopy structure of human LRRC8A that displays well-resolved NTs. Amino-terminal halves of NTs fold back into the pore and constrict the permeation path, thereby determining ion selectivity together with an extracellular selectivity filter with which it works in series. They also interact with pore-surrounding helices and support their compact arrangement. The C-terminal halves of NTs interact with intracellular loops that are crucial for channel activation. Molecular dynamics simulations indicate that low ionic strength increases NT mobility and expands the radial distance between pore-surrounding helices. Our work suggests an unusual pore architecture with two selectivity filters in series and a mechanism for VRAC activation by cell swelling.
容积调节阴离子通道 (VRAC) 是由 LRRC8 蛋白组成的六聚体，对于细胞体积调节至关重要。必需的 LRRC8A 亚基的 N 端 (NTs) 调节 VRAC 的激活和离子选择性，但潜在的机制仍知之甚少。在这里，我们报告了人类 LRRC8A 的 2.8Å 冷冻电镜结构，该结构显示出分辨率良好的 NTs。NTs 的氨基端折叠回孔内并收缩渗透路径，从而与细胞外选择性过滤器一起确定离子选择性，后者与它串联工作。它们还与孔周围的螺旋相互作用并支持其紧密排列。NTs 的 C 端与对通道激活至关重要的细胞内环相互作用。分子动力学模拟表明，低离子强度会增加 NT 的迁移率并扩大孔周围螺旋之间的径向距离。我们的工作表明存在一种不寻常的孔结构，其中有两个串联的选择性过滤器，以及细胞肿胀激活 VRAC 的机制。
