Department of Neuroscience, Howard Hughes Medical Institute, The Scripps Research Institute, La Jolla, United States.
Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, United States.
Elife. 2018 Aug 10;7:e38461. doi: 10.7554/eLife.38461.
SWELL1 (LRRC8A) is the only essential subunit of the Volume Regulated Anion Channel (VRAC), which regulates cellular volume homeostasis and is activated by hypotonic solutions. SWELL1, together with four other LRRC8 family members, potentially forms a vastly heterogeneous cohort of VRAC channels with different properties; however, SWELL1 alone is also functional. Here, we report a high-resolution cryo-electron microscopy structure of full-length human homo-hexameric SWELL1. The structure reveals a trimer of dimers assembly with symmetry mismatch between the pore-forming domain and the cytosolic leucine-rich repeat (LRR) domains. Importantly, mutational analysis demonstrates that a charged residue at the narrowest constriction of the homomeric channel is an important pore determinant of heteromeric VRAC. Additionally, a mutation in the flexible N-terminal portion of SWELL1 affects pore properties, suggesting a putative link between intracellular structures and channel regulation. This structure provides a scaffold for further dissecting the heterogeneity and mechanism of activation of VRAC.
水通道蛋白 1（LRRC8A）是容积调节阴离子通道（VRAC）的唯一必需亚基，调节细胞体积平衡，被低渗溶液激活。SWELL1 与其他四个 LRRC8 家族成员一起，可能形成具有不同特性的 VRAC 通道的巨大异质群体；然而，SWELL1 本身也是功能性的。在这里，我们报告了全长人同源六聚体 SWELL1 的高分辨率冷冻电镜结构。该结构揭示了三聚体二聚体的组装，其中孔形成结构域和细胞质富含亮氨酸重复（LRR）结构域之间存在对称性不匹配。重要的是，突变分析表明，同型通道最狭窄收缩处的带电残基是异源 VRAC 的重要孔决定因素。此外，SWELL1 的柔性 N 端部分的突变会影响孔特性，这表明细胞内结构和通道调节之间存在潜在联系。该结构为进一步剖析 VRAC 的异质性和激活机制提供了一个支架。
