Gating and Regulation of Connexin Hemichannels

描述（由申请人提供）：连接蛋白蛋白中的点突变可导致半通道功能的增加（例如，加重的半通道开放），其导致人类病理学，包括耳聋、皮肤病、白内障和腓骨肌萎缩症。由于水孔的大尺寸和适度的选择性，质膜处连接蛋白半通道的加剧开放导致电化学梯度和小细胞质代谢物的损失，从而导致细胞死亡。半通道开放的控制是必不可少的，并且是通过生理性细胞外Ca 2+来实现的，这大大降低了半通道活性。由连接蛋白突变引起的异常开放的半通道对细胞外Ca 2+不太敏感。这些突变中的一些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Ca 2+结合位点本身。为了解释这些突变和半通道中Ca 2+调节之间的关系，我们假设Ca 2+结合并稳定封闭的半通道。产生功能增益的突变减少了闭合状态的占用，使通道对Ca 2+不太敏感。本项目的目标是确定外部Ca 2+调节连接蛋白半通道的分子基础，以及导致疾病的人类连接蛋白26（hCx 26）突变诱导的半通道功能获得的机制基础。最近解决了hCx 26通道的晶体结构，并将作为结构-功能研究的指导。我们希望更好地了解连接蛋白通道的门控和Ca 2+调节机制，将导致开发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的获得，并希望在hCx 26的情况下，用于治疗由这种连接蛋白突变引起的耳聋和皮肤病。

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.