连接蛋白(Cxs)是一个完整的膜蛋白家族,既充当六聚体半通道(HCs)又充当十二聚体间隙连接通道(GJCs),充当细胞之间以及细胞和细胞外环境之间的电和分子通信的管道,分别。它们的正常运作对许多过程至关重要,包括发展,生理学,以及对疾病和创伤的反应。异常的GJC和HC通信可导致许多病理状态,包括炎症,皮肤病,耳聋,神经系统疾病,和心律失常.在过去的15年里,七个Cx同工型的高分辨率X射线和电子低温显微镜(cryoEM)结构揭示了每个亚基的四螺旋跨膜(TM)束的保守性;二硫键连接的胞外环中的αβ折叠和跨细胞外间隙的亚基间氢键,介导端对端对接以在GJC的六聚体之间形成紧密密封。组织损伤与细胞Ca2+过载有关。令人惊讶的是,12个Ca2+离子在Cx26GJC中的结合产生了一种新的阻止阳离子渗透的静电门控机制。相比之下,组织损伤过程中的酸性pH会引起N端(NT)结构域的缔合,这些结构域以“球链”方式在空间上阻塞孔。生理条件下的NT结构域表现出多种构象状态,由蛋白质-蛋白质和蛋白质-脂质相互作用稳定,这可能与门控机制有关。冷冻EM图还显示了孔内推定的脂质密度,插入跨膜α-螺旋和质子之间,它的功能是未知的。为了未来,分离的Cx通道的时间分辨冷冻EM以及细胞和组织中GJCs和HC的冷冻断层扫描将对通道调节机制有更深入的了解。细胞质环(CL)和C端(CT)结构域在序列和长度上是不同的,可能参与渠道监管,但是由于构象的灵活性,在高分辨率X射线和冷冻EM图中无法可视化。我们预计,协同物理化学的综合利用,光谱学,生物物理,和计算方法将揭示与功能状态相关的构象动力学。我们预计,在不同的病理条件下,如此丰富的结果将加速与Cx通道调制相关的药物发现。
Connexins (Cxs) are a family of integral membrane proteins, which function as both hexameric hemichannels (HCs) and dodecameric gap junction channels (GJCs), behaving as conduits for the electrical and molecular communication between cells and between cells and the extracellular environment, respectively. Their proper functioning is crucial for many processes, including development, physiology, and response to disease and trauma. Abnormal GJC and HC communication can lead to numerous pathological states including inflammation, skin diseases, deafness, nervous system disorders, and cardiac arrhythmias. Over the last 15 years, high-resolution X-ray and electron cryomicroscopy (cryoEM) structures for seven Cx isoforms have revealed conservation in the four-helix transmembrane (TM) bundle of each subunit; an αβ fold in the disulfide-bonded extracellular loops and inter-subunit hydrogen bonding across the extracellular gap that mediates end-to-end docking to form a tight seal between hexamers in the GJC. Tissue injury is associated with cellular Ca2+ overload. Surprisingly, the binding of 12 Ca2+ ions in the Cx26 GJC results in a novel electrostatic gating mechanism that blocks cation permeation. In contrast, acidic pH during tissue injury elicits association of the N-terminal (NT) domains that sterically blocks the pore in a \"ball-and-chain\" fashion. The NT domains under physiologic conditions display multiple conformational states, stabilized by protein-protein and protein-lipid interactions, which may relate to gating mechanisms. The cryoEM maps also revealed putative lipid densities within the pore, intercalated among transmembrane α-helices and between protomers, the functions of which are unknown. For the future, time-resolved cryoEM of isolated Cx channels as well as cryotomography of GJCs and HCs in cells and tissues will yield a deeper insight into the mechanisms for channel regulation. The cytoplasmic loop (CL) and C-terminal (CT) domains are divergent in sequence and length, are likely involved in channel regulation, but are not visualized in the high-resolution X-ray and cryoEM maps presumably due to conformational flexibility. We expect that the integrated use of synergistic physicochemical, spectroscopic, biophysical, and computational methods will reveal conformational dynamics relevant to functional states. We anticipate that such a wealth of results under different pathologic conditions will accelerate drug discovery related to Cx channel modulation.