Volume-regulated anion channels (VRACs) are multimeric proteins composed of different paralogs of the LRRC8 family. They are activated in response to hypotonic swelling, but little is known about their specific functions. We studied two human individuals with the same congenital syndrome affecting blood vessels, brain, eyes, and bones. The LRRC8C gene harbored de novo variants in both patients, located in a region of the gene encoding the boundary between the pore and a cytoplasmic domain, which is depleted of sequence variations in control subjects. When studied by cryo-EM, both LRRC8C mutant proteins assembled as their wild-type counterparts, but showed increased flexibility, suggesting a destabilization of subunit interactions. When co-expressed with the obligatory LRRC8A subunit, the mutants exhibited enhanced activation, resulting in channel activity even at isotonic conditions in which wild-type channels are closed. We conclude that structural perturbations of LRRC8C impair channel gating and constitute the mechanistic basis of the dominant gain-of-function effect of these pathogenic variants. The pleiotropic phenotype of this novel clinical entity associated with monoallelic LRRC8C variants indicates the fundamental roles of VRACs in different tissues and organs.

中文翻译：

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LRRC8C 中的从头变异导致组成型通道激活，导致人类多系统紊乱。


体积调节阴离子通道 （VRAC） 是由 LRRC8 家族的不同旁系同源物组成的多聚体蛋白。它们因低渗肿胀而被激活，但对其具体功能知之甚少。我们研究了两个患有相同先天性综合征的人类个体，这些综合征影响血管、大脑、眼睛和骨骼。LRRC8C 基因在两名患者中都带有从头变异，位于编码孔和细胞质结构域之间边界的基因区域，该区域在对照受试者中耗尽了序列变异。当通过冷冻电镜研究时，两种 LRRC8C 突变蛋白都像野生型对应物一样组装，但显示出更高的灵活性，表明亚基相互作用不稳定。当与强制性 LRRC8A 亚基共表达时，突变体表现出增强的激活，即使在野生型通道关闭的等渗条件下也产生通道活性。我们得出结论，LRRC8C 的结构扰动损害了通道门控，并构成了这些致病性变体的主要功能增益效应的机制基础。这种与单等位基因 LRRC8C 变体相关的新临床实体的多效性表型表明 VRAC 在不同组织和器官中的基本作用。