The fluorescent protein (FP) color palette has greatly contributed to the visualization of molecular and cellular processes. However, most FPs lose fluorescence at a pH lower than their neutral pKa(∼6), and this has hampered their application in acidic organelles (pH ∼4.5–6.0). Currently, several cyan- and red-colored acid-tolerant FPs are available; however, there are few reports of acid-tolerant green FPs (GFPs) that are practically applicable to bioimaging. Here, we developed the acid-tolerant monomeric GFP “Gamillus” from the jellyfishOlindias formosa, with excellent brightness, maturation speed, and photostability. Results from X-ray crystallography and point mutagenesis suggest that across a broad pH range the acid tolerance is attributed to stabilization of deprotonation in the chromophore phenyl ring by forming a uniquetransconfiguration. We demonstrate that Gamillus can serve as a molecular tag suitable for imaging in acidic organelles through autophagy-mediated molecular tracking to lysosomes.

中文翻译：

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福尔摩斯（Olindias formosa）的耐酸单体GFP

荧光蛋白（FP）调色板极大地促进了分子和细胞过程的可视化。但是，大多数FP在低于其中性pKa（〜6）的pH值下会丢失荧光，这阻碍了它们在酸性细胞器（pH值〜4.5-6.0）中的应用。当前，有几种青色和红色的耐酸FP。但是，几乎没有关于耐酸的绿色FP（GFP）的报道可用于生物成像。在这里，我们从海fromOlindias formosa开发了耐酸单体GFP“ Gamillus”，具有出色的亮度，成熟速度和光稳定性。X射线晶体学和点诱变的结果表明，在宽的pH范围内，酸耐受性归因于发色团苯环中去质子化的稳定作用，形成了独特的反式构型。