Though the concentration of chloride has been measured in the cytoplasm and in secretory granules of live cells, it cannot be measured within the endoplasmic reticulum (ER) due to poor fluorescence of existing biosensors. We developed a fluorescent biosensor composed of a chloride-sensitive superfolder GFP and long Stokes-shifted mKate2 for simultaneous chloride and pH measurements that retained fluorescence in the ER lumen. Using this sensor, we showed that the chloride concentration in the ER is significantly lower than that in the cytosol. This improved biosensor enables dynamic measurement of chloride in the ER and may be useful in other environments where protein folding is challenging.

中文翻译：

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基于超文件夹绿色荧光蛋白的生物传感器可以监测内质网中的氯离子

虽然已经在活细胞的细胞质和分泌颗粒中测量了氯化物的浓度，但由于现有生物传感器的荧光较差，因此无法在内质网 (ER) 内测量。我们开发了一种荧光生物传感器，由对氯离子敏感的超级文件夹 GFP 和长斯托克斯位移 mKate2 组成，用于同时测量氯离子和 pH 值，在 ER 腔中保留荧光。使用该传感器，我们发现 ER 中的氯化物浓度明显低于胞质溶胶中的氯化物浓度。这种改进的生物传感器能够动态测量 ER 中的氯化物，并且可能在蛋白质折叠具有挑战性的其他环境中有用。