PDF(Pubmed)
Abstract：
Connexins allow intercellular communication by forming gap junction channels (GJCs) between juxtaposed cells. Connexin26 (Cx26) can be regulated directly by CO2. This is proposed to be mediated through carbamylation of K125. We show that mutating K125 to glutamate, mimicking the negative charge of carbamylation, causes Cx26 GJCs to be constitutively closed. Through cryo-EM we observe that the K125E mutation pushes a conformational equilibrium towards the channel having a constricted pore entrance, similar to effects seen on raising the partial pressure of CO2. In previous structures of connexins, the cytoplasmic loop, important in regulation and where K125 is located, is disordered. Through further cryo-EM studies we trap distinct states of Cx26 and observe density for the cytoplasmic loop. The interplay between the position of this loop, the conformations of the transmembrane helices and the position of the N-terminal helix, which controls the aperture to the pore, provides a mechanism for regulation.
摘要：
连接蛋白通过在并列的细胞之间形成间隙连接通道（GJC）来允许细胞间通讯。连接蛋白26(Cx26)可直接受CO2调节。这被认为是通过K125的氨基甲酰化来介导的。我们证明K125突变成谷氨酸，模仿氨基甲酰化的负电荷，导致Cx26GJC组成关闭。通过cryo-EM，我们观察到K125E突变将构象平衡推向具有收缩孔入口的通道，类似于提高二氧化碳分压的效果。在以前的连接蛋白结构中，细胞质环，在监管和K125所在的地方很重要，是无序的。通过进一步的低温EM研究，我们捕获了Cx26的不同状态，并观察了细胞质环的密度。这个循环的位置之间的相互作用，跨膜螺旋的构象和N末端螺旋的位置，控制毛孔的孔径，提供了一种监管机制。
