Blue light changes a fluorophore from green to red

During the past several years, researchers have developed photoactivatable fluorescent proteins that are similar to GFP but that change color when introduced to UV-to-violet wavelengths. Unfortunately, UV radiation can be damaging to some of the biological entities one might wish to study.

Now scientists at the Russian Academy of Sciences in Moscow have created a fluorescent protein, dubbed Dendra, that can convert from green to red with 1000 to 4500 times efficiency using a blue laser.

A confocal image shows a cell with Dendra-tagged proteins concentrated in nucleoli. When activated by a pulse from a 488-nm laser, the upper nucleolus became red. Courtesy of Konstantin Lukyanov.

The researchers, led by brothers Sergey and Konstantin Lukyanov, report in the April issue of Nature Biotechnology that they mutated Dendra from a GFP-like molecule found in a nonluminescent sea coral. They used a fluorescence stereomicroscope to screen the bacterial colonies that expressed the variations and a fluorescence spectrophotometer to measure the quantum yield, which was 0.72 when green or 0.70 when red. They also found that the protein is very stable, making it suitable for long-term protein tracking.

To test Dendra’s capabilities, the scientists expressed it in live cells as conjugates with various proteins. They exposed conjugates to the light generated by either a 125-mW argon or a 1-mW HeNe laser. The protein changed from green to red when the 488-nm laser beam intensity was 0.5 to 0.7 W/cm², but no conversion occurred when the intensity was <50 mW/cm².