(Image: Roberto Sozzani)
Russian researchers affiliated with the Howard Hughes Medical Institute have developed a red fluorescent protein that is 7-10 times brighter than any other red fluorescent protein currently being used for imaging.
The protein, which has been named Katushka, is derived from a brilliant red sea anemone (Entacmaea quadricolor, the blue tip anemone, above) bought by one of the researchers from a pet shop in Moscow.
After acquiring the specimen, co-author Sergey Lukyanov took it to his laboratory, where he and his colleagues isolated the red protein. They cloned the gene and developed an enhanced, brighter version, turbo red fluorescent protein (TurboRFP), which was about twice as bright as DsRed2, the brightest red fluorescent protein currently available.
They then created about 100,000 variants of the RFP gene by introducing random mutations into the DNA sequence, and screened all of the resulting proteins for brightness.
One of the variants – Katushka – was found to be up to 10 times brighter than the DsRed2. The image below shows 2.5 month old embryos of the African clawed toad Xenopus laevis; the one on the left expresses Katushka, and the one on the right expresses DsRed2.
Green fluorescent protein was originally isolated in the early 1960s, from the jellyfish Aquoria victoria. The subsequent cloning of the GFP gene led to a revolution in bioimaging – fluorescence microscopy is now an indespensible tool for cellular and developmental biologists.
In fact, reasearchers now have a whole rainbow of fluorescences with which they can investigate cellular and subcellular processes. But Katushka has a unique combination of features which will make it a valuable addition to researcher’s fluorescent palette.
The protein fluoresces very brightly, far more so than other proteins that emit fluorescence of a “far-red” wavelength. Because of the long wavelength, the fluoresence can pass through tissues easily. This means that the Katushka protein will be extremely useful a marker for whole-body fluorescence imaging, in, for example, animal embryos that are not transparent.
Also, the chromophore of the Katushka protein matures more rapidly than that of any other fluorescent protein. The chromophore is that part of the protein that causes the molecule to change shape when struck by light; this conformational change leads to the emission of fluorescence. This will enable researchers to investigate events at even earlier stages of development than was previously possible.
Shcherbo, D., et al. (2007). Bright far-red fluorescent protein for whole-body imaging. Nat. Methods doi: doi:10.1038/nmeth1083. [Abstract]