Data from: The first extracellular domain plays an important role in unitary channel conductance of Cx50 gap junction channels

Gap junction (GJ) channels provide direct passage for ions and small molecules to be exchanged between neighbouring cells and are crucial for many physiological processes. GJ channels can be gated by transjunctional voltage (known as Vj-gating) and display a wide range of unitary channel conductance (γj), yet the domains responsible for Vj-gating and γj are not fully clear. The first extracellular domain (E1) of several connexins has been shown to line part of their GJ channel pore and play important roles in Vj-gating properties and/or ion permeation selectivity. To test roles of the E1 of Cx50 GJ channels, we generated a chimera, Cx50Cx36E1, where the E1 domain of Cx50 was replaced with that of Cx36, a connexin showing quite distinct Vj-gating and γj from those of Cx50. Detailed characterizations of the chimera and three point mutants in E1 revealed that, although the E1 domain is important in determining γj, the E1 domain of Cx36 is able to effectively function within the context of the Cx50 channel with minor changes in Vj-gating properties, indicating that sequence differences between the E1 domains in Cx36 and Cx50 cannot account for their drastic differences in Vj-gating and γj. Our homology models of the chimera and the E1 mutants revealed that electrostatic properties of the pore-lining residues and their contribution to the electric field in the pore are important factors for the rate of ion permeation of Cx50 and possibly other GJ channels.间隙连接（Gap Junction，GJ）通道可介导相邻细胞间离子与小分子的直接交换，对众多生理过程至关重要。GJ通道可受跨连接电压（transjunctional voltage，又称Vj门控）调控，并展现出宽泛的单通道电导（unitary channel conductance，γj）分布范围，然而负责Vj门控与单通道电导的结构域尚未完全阐明。已有研究证实，多种连接蛋白（connexin）的第一个胞外结构域（E1）可构成GJ通道孔道的部分内衬，并在Vj门控特性以及离子渗透选择性中发挥关键作用。为探究连接蛋白50（Cx50）GJ通道E1结构域的功能，我们构建了嵌合体Cx50Cx36E1，即将Cx50的E1结构域替换为连接蛋白36（Cx36）的E1结构域——Cx36是一种与Cx50在Vj门控与单通道电导特性上差异显著的连接蛋白。对该嵌合体以及三个E1区域点突变体的详细表征结果显示，尽管E1结构域对单通道电导的确定具有重要意义，但Cx36的E1结构域可在Cx50通道的框架内有效行使功能，仅伴随Vj门控特性的轻微改变，这表明Cx36与Cx50的E1结构域间的序列差异，无法解释二者在Vj门控与单通道电导上的显著差异。我们对该嵌合体及E1突变体的同源建模（homology model）分析显示，孔道内衬残基的静电特性及其对孔道内电场的贡献，是影响Cx50乃至其他GJ通道离子渗透速率的关键因素。