Serendipitous crystal structure of mJuniper, a rationally designed cyan fluorescent protein

mJuniper is a recently developed monomeric cyan fluorescent protein (CFP) optimized for bacterial imaging, distinguished by the fastest maturation kinetics recorded for a CFP. mJuniper shows significant promise for time-lapse microscopy, but was used here to improve the solubility of a target protein. Here, we report the high-resolution X-ray structure of mJuniper, obtained serendipitously during an attempted structural characterization of CagG, an essential component of the Helicobacter pylori Cag type IV secretion system. The structure reveals a classical β-barrel scaffold, as well as a chromophore with two rotameric states, resulting from specific radiation damage occurring in its vicinity.