Shinoda, H. et al. Cell Chem. Biol. 25, 330–338 (2018).

Fluorescent proteins such as GFP are invaluable for imaging proteins. However, the acidic environment in organelles of the secretory pathway is not conducive for many fluorescent proteins, especially those of the green variety. Shinoda et al. have discovered a new GFP from the jellyfish Olindias formosa that has limited sequence homology to other GFPs. In contrast to available GFPs, the new variant turned out to be highly acid tolerant. Via both rational design and directed evolution, the researchers monomerized the original protein and increased its solubility and brightness to generate the final GFP, which they called Gamillus. Gamillus is about half as bright as EGFP in HeLa cells and performs well in a variety of fusion proteins. Importantly, Gamillus retains its fluorescence in lysosomes and should therefore be a useful tool for studying the secretory pathway.