Blue light changes a fluorophore from green to red
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
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.
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