Conformational changes in CIC chloride transporters

本项目继续研究ClC型氯离子通道蛋白的构象变化。氯离子传导离子通道的CLC家族参与许多生物过程;这些通道维持骨骼肌中的静息膜电位，调节中枢神经元的兴奋性，并参与各种细胞内隔室中pH的稳态。尽管它们的生理重要性，这些通道的功能机制知之甚少。我们正试图了解这些蛋白质的功能特性，通过检查几个家庭成员，包括真核和原核同源物。 我们目前在这一领域的重点是观察流量由于一个单一的CLC转运蛋白在一个单一的蛋白脂质体。我们正在与哥本哈根大学的Dimitrios Stamou合作使用单分子方法进行研究。为此，我们已经开发了一个强大的批量测定氯离子耦合质子运输，然后进行个别脂质体类似的条件。我们现在已经可重复地观察到单个脂质体中的CLC介导的通量，并观察到复杂的pH变化，这表明目前的模型不能完全解释CLC蛋白的功能。此外，在过去的一年里，我们一直在探索另一种Clc，ClC-7的患者突变，这在溶酶体酸化中很重要。这种突变导致的疾病不同于其他ClC缺陷引起的疾病。我们一直在研究突变的功能影响，通过表达野生型和突变蛋白（与额外的突变，重新定位蛋白质的细胞表面）在非洲爪蟾卵母细胞和分析所产生的电流的特性。这些结果有助于深入了解患者缺陷的机制及其潜在的蛋白质原因。

This project continued studying conformational changes in ClC-type chloride channel proteins. The ClC family of chloride-conducting ion channels is involved in a host of biological processes; these channels maintain the resting membrane potential in skeletal muscle, modulate excitability in central neurons, and are involved in the homeostasis of pH in a variety of intracellular compartments. Despite their physiological importance, the mechanisms by which these channels function are poorly understood. We are attempting to understand the functional properties of these proteins by examining several family members, including both eukaryotic and prokaryotic homologs. Our current focus in this area is to observe the flux due to a single ClC transporter in a single proteoliposome. We are doing this using single molecule methods in collaboration with Dimitrios Stamou at the University of Copenhagen. Toward this end we have developed a robust bulk assay of chloride-coupled proton transport, and then subjected individual liposomes to similar conditions. We have now reproducibly observed ClC-mediated fluxes in individual liposomes and have obeserved complex pH variation, suggesting that current models do not fully explain the function of the CLC protein. IN addition, over the past year we have been exploring a patient mutation in another Clc, ClC-7, which is important in lysosomal acidification. THis mutation leads to a disease different from those caused by other ClC defects. We have been investigating the functional effects of the mutation by expressing WT and mutant proteins (with additional mutations that retarget the protein to the cell surface) in Xenopus oocytes and analyzing the properties of the resulting currents. These results give insight into the mechanism of the defect in patients and its underlying protein cause.