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强(例如，加剧半通道开放)，从而导致人类病理，包括耳聋、皮肤病、白内障和夏科-玛丽-图斯病。由于水孔的大小和适度的选择性，细胞质膜上连接蛋白半通道的开放加剧导致电化学梯度的丧失和小的细胞质代谢物的丢失，导致细胞死亡。控制半通道的开放是必不可少的，这是通过生理性的细胞外钙离子来实现的，它大大降低了半通道的活性。由连接蛋白突变引起的异常开放的半通道对细胞外钙离子不那么敏感。其中一些突变位于毛孔的细胞内部位末端，这表明它们影响的是门控(毛孔的打开和关闭)，而不是钙结合部位本身。为了解释这些突变与半通道中钙离子调节之间的关系，我们假设钙离子与闭合的半通道结合并稳定。产生功能增益的突变会减少闭合状态的占有率，使通道对钙离子不那么敏感。本项目的目标是确定外源钙离子对连接蛋白半通道的调控的分子基础，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被解决，并将作为结构-功能研究的指南。我们希望更好地理解连接蛋白通道的门控和钙调节机制将导致药物和其他治疗方法的发展，这些药物和其他治疗方法可以特异性地纠正或补偿半通道功能获得，并有望以hCx26为例，用于治疗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.