Gating and Regulation of Connexin Hemichannels

描述（由申请人提供）：连接蛋白的点突变可导致半通道功能增加（例如，半通道开放加剧），从而导致人类病理，包括耳聋、皮肤病、白内障和沙克-玛丽-图斯病。由于水孔的大尺寸和适度的选择性，质膜上连接蛋白半通道的加速开放导致电化学梯度和小细胞质代谢物的损失，导致细胞死亡。控制半通道开放是必不可少的，并通过生理细胞外Ca2+，这大大降低了半通道活性实现。连接蛋白突变引起的异常开放的半通道对细胞外Ca2+不太敏感。其中一些突变位于孔的细胞内位点末端，表明它们影响门控（孔的打开和关闭）而不是Ca2+结合位点本身。为了解释这些突变和Ca2+在半通道中的调节之间的关系，我们假设Ca2+结合并稳定封闭的半通道。产生功能增益的突变减少了封闭状态的占用，使通道对Ca2+不那么敏感。本项目的目标是确定外源性Ca2+调控连接蛋白半通道的分子基础，以及人类连接蛋白26 （hCx26）突变导致疾病的半通道功能获得的机制基础。hCx26通道的晶体结构最近得到了解决，将为结构-功能研究提供指导。我们希望更好地了解门控和Ca2+调节连接蛋白通道的机制，将导致药物和其他治疗方法的发展，可以特异性地纠正或补偿半通道的功能增益，并希望在hCx26的情况下，治疗由这种连接蛋白突变引起的耳聋和皮肤疾病。

DESCRIPTION (provided by applicant): Point mutations in connexin proteins can cause gain in hemichannel function (e.g., exacerbated hemichannel opening), which results in human pathologies, including deafness, skin disorders, cataract and Charcot-Marie-Tooth disease. Due to the large size and modest selectivity of the aqueous pore, exacerbated opening of connexin hemichannels at the plasma membrane leads to loss of electrochemical gradients and of small cytoplasmic metabolites, causing cell death. Control of hemichannel opening is indispensable, and is achieved by physiological extracellular Ca2+, which drastically reduces hemichannel activity. Aberrantly open hemichannels caused by connexin mutations are less sensitive to extracellular Ca2+. Some of these mutations are located at the intracellular site end of the pore, suggesting that they affect gating (opening and closing of the pore) rather than the Ca2+ binding site itself. To explain the relationship between these mutations and Ca2+ regulation in hemichannels, we hypothesize that Ca2+ binds to and stabilizes the closed hemichannel. Mutations that produce gain of function decrease occupancy of the closed state, rendering the channel less sensitive to Ca2+. The goal of this project is to identify the molecular basis of regulation of connexin hemichannels by external Ca2+ and the mechanistic basis of hemichannel gain of function induced by mutations in human connexin26 (hCx26) that cause disease. The crystal structure of the hCx26 channel was recently solved and will serve as a guide for structure-function studies. We hope that a better understanding of the mechanisms of gating and Ca2+ regulation of connexin channels will lead to development of drugs and other therapeutic approaches that can specifically correct or compensate for hemichannel gain of function, and hopefully serve, in the case of hCx26, to treat deafness and skin disorders caused by mutation of this connexin.