State Key Laboratory of Medicinal Chemical Biology and College of Life Sciences, Nankai University, Tianjin, China.
School of Medicine, Zhejiang University, Hangzhou, China.
PLoS Biol. 2019 Apr 22;17(4):e3000096. doi: 10.1371/journal.pbio.3000096. eCollection 2019 Apr.
The Orai channel is characterized by voltage independence, low conductance, and high Ca2+ selectivity and plays an important role in Ca2+ influx through the plasma membrane (PM). How the channel is activated and promotes Ca2+ permeation is not well understood. Here, we report the crystal structure and cryo-electron microscopy (cryo-EM) reconstruction of a Drosophila melanogaster Orai (dOrai) mutant (P288L) channel that is constitutively active according to electrophysiology. The open state of the Orai channel showed a hexameric assembly in which 6 transmembrane 1 (TM1) helices in the center form the ion-conducting pore, and 6 TM4 helices in the periphery form extended long helices. Orai channel activation requires conformational transduction from TM4 to TM1 and eventually causes the basic section of TM1 to twist outward. The wider pore on the cytosolic side aggregates anions to increase the potential gradient across the membrane and thus facilitate Ca2+ permeation. The open-state structure of the Orai channel offers insights into channel assembly, channel activation, and Ca2+ permeation.
Orai 通道的特点是电压独立性、低电导和高 Ca2+选择性，在通过质膜（PM）的 Ca2+内流中发挥重要作用。通道如何被激活并促进 Ca2+渗透尚不清楚。在这里，我们报告了果蝇 Orai（dOrai）突变体（P288L）通道的晶体结构和低温电子显微镜（cryo-EM）重建，该通道根据电生理学显示为组成型激活。Orai 通道的开放状态显示出六聚体组装，其中中心的 6 个跨膜 1（TM1）螺旋形成离子传导孔，而外围的 6 个 TM4 螺旋形成延伸的长螺旋。Orai 通道的激活需要从 TM4 到 TM1 的构象转导，最终导致 TM1 的碱性部分向外扭曲。细胞质侧较宽的孔聚集阴离子以增加跨膜的电势梯度，从而促进 Ca2+渗透。Orai 通道的开放状态结构提供了对通道组装、通道激活和 Ca2+渗透的深入了解。
