To mediate cell-to-cell communication via gap junction channels (GJCs), connexins (Cx) traffic as hexameric hemichannels to the plasma membrane, which dock end-to-end between adjacent cell membranes, thereby forming a dodecameric intercellular conduit. Hemichannels also function independently to mediate the passage of contents between the cytoplasm and extracellular space. To generate hemichannels, the mutation N176Y was introduced into the second extracellular loop of Cx26. The electron cryomicroscopy structure of the hexameric hemichannel in lipid bilayer nanodiscs displays an open pore and a 4-helix bundle transmembrane design that is nearly identical to dodecameric GJCs. In contrast to the high resolution of the transmembrane α-helices, the extracellular loops are less well resolved. The conformational flexibility of the extracellular loops may be essential to facilitate surveillance of hemichannels in apposed cells to identify compatible Cx isoforms that enable intercellular docking. Our results also provide a structural foundation for previous electrophysiologic and permeation studies of Cx hemichannels.

为了通过间隙连接通道 (GJC) 介导细胞间通讯，连接蛋白 (Cx) 作为六聚体半通道运输至质膜，在相邻细胞膜之间端到端对接，从而形成十二聚体细胞间导管。半通道还独立发挥作用，介导细胞质和细胞外空间之间内容物的通过。为了产生半通道，将突变 N176Y 引入 Cx26 的第二个细胞外环中。脂质双层纳米盘中六聚体半通道的电子冷冻显微镜结构显示出开放孔和四螺旋束跨膜设计，与十二聚体 GJC 几乎相同。与跨膜 α 螺旋的高分辨率相比，细胞外环的分辨率较差。细胞外环的构象灵活性对于促进对并列细胞中的半通道的监视以识别能够实现细胞间对接的相容的 Cx 亚型可能至关重要。我们的结果还为之前的 Cx 半通道电生理学和渗透研究提供了结构基础。