Study of the on-off photoswitching of mEmerald at cryogenic temperature

mEmerald is a GFP-derived fluorescent protein that showed a tendency to reversibly photoswitch between an "on" fluorescent state and an "off" non-fluorescent state under cryogenic conditions. It has been used to this purpose in super-resolution PALM imaging. Usually, reversibly switchable fluorecent proteins (RSFPs) photoswitch via the ci-trans isomerization of their chromophore. Such major reorganizations are prevented by cryogenic conditions and the efficient roomtemperature photoswitching of most of the existing RSFPs is abolished at low temperatures. mEmerald seems to be one of the rare exceptions but its photophysical mechanism remains to be elucidated. After having solved the high resolution 3D structure of the initial green-emiting form of the protein, I would like to solve the structure of photoswitched form at cryogenic temperature (100K), and correlate this structure with the corresponding absorption and/or emission spectra either measured offline or, if possible, online.