Department of Ophthalmology, Columbia University, New York, NY, USA.
Department of Pharmacology, Columbia University, New York, NY, USA.
Nat Commun. 2022 Jul 4;13(1):3836. doi: 10.1038/s41467-022-31437-7.
Bestrophin-1 (Best1) and bestrophin-2 (Best2) are two members of the bestrophin family of calcium (Ca)-activated chloride (Cl) channels with critical involvement in ocular physiology and direct pathological relevance. Here, we report cryo-EM structures of wild-type human Best1 and Best2 in various states at up to 1.8 Å resolution. Ca-bound Best1 structures illustrate partially open conformations at the two Ca-dependent gates of the channels, in contrast to the fully open conformations observed in Ca-bound Best2, which is in accord with the significantly smaller currents conducted by Best1 in electrophysiological recordings. Comparison of the closed and open states reveals a C-terminal auto-inhibitory segment (AS), which constricts the channel concentrically by wrapping around the channel periphery in an inter-protomer manner and must be released to allow channel opening. Our results demonstrate that removing the AS from Best1 and Best2 results in truncation mutants with similar activities, while swapping the AS between Best1 and Best2 results in chimeric mutants with swapped activities, underlying a key role of the AS in determining paralog specificity among bestrophins.
Bestrophin-1（Best1）和 Bestrophin-2（Best2）是 Bestrophin 家族的两个成员，是钙（Ca）激活氯离子（Cl）通道，在眼部生理学中具有关键作用，并且与直接的病理学相关。在这里，我们报告了野生型人 Best1 和 Best2 在各种状态下的冷冻电镜结构，分辨率高达 1.8Å。结合 Ca 的 Best1 结构说明了通道的两个 Ca 依赖性门的部分开放构象，而结合 Ca 的 Best2 则观察到完全开放的构象，这与 Best1 在电生理记录中传导的电流明显较小一致。对比关闭和开放状态揭示了一个 C 端自动抑制片段（AS），它通过以相互体方式缠绕在通道周围来同心地收缩通道，并必须释放以允许通道打开。我们的结果表明，从 Best1 和 Best2 中去除 AS 会导致具有相似活性的截断突变体，而在 Best1 和 Best2 之间交换 AS 会导致活性交换的嵌合突变体，这表明 AS 在决定 Bestrophin 之间的同种蛋白特异性方面起着关键作用。
