Kaede is a photoactivatable fluorescent protein naturally originated from a stony coral, Trachyphyllia geoffroyi.
This tetramerization possibly makes Kaede have a low tendency to form aggregates when fused to other proteins.
The property of photoconverted fluorescence Kaede protein was serendipitously discovered and first reported by Ando et al. in Proceedings of the United States National Academy of Sciences.
[1] An aliquot of Kaede protein was discovered to emit red fluorescence after being left on the bench and exposed to sunlight.
The property of photoconversion in Kaede is contributed by the tripeptide, His62-Tyr63-Gly64, that acts as a green chromophore that can be converted to red.
When exposed to UV, Kaede protein undergoes unconventional cleavage between the amide nitrogen and the α carbon (Cα) at His62 via a formal β-elimination reaction.
A reduced fluorescence is observed in red, photoconverted Kaede when it is intensively exposed to 405 nm light, followed by partial recover after several minutes.
Even when cultured neurons are labeled with fluorescent proteins, they are still difficult to identify individually because of the dense package.
Due to the special property of photo-switchable fluorescence, Kaede protein possesses several advantages as an optical cell marker.
[1] Besides, before the photoconversion, Kaede emits bright green fluorescence which enables the visualization of the localization of the non-photoacivated protein.
The photoconversion property of Kaede does not only contribute to the application on protein labeling and cell tracking, it is also responsible for the vast variation in the colour of stony corals, Trachyphyllia geoffroyi.