Tryptophan-based chromophore in fluorescent proteins can be anionic.
Karen S Sarkisyan1, Ilia V Yampolsky, Kyril M Solntsev
1Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Moscow, Russia.
Scientific Reports
|August 31, 2012
Summary
Researchers discovered that cyan fluorescent proteins (CFP) can emit green light when their tryptophan chromophore becomes deprotonated, creating an anionic state. This finding opens new avenues for controlling fluorescent protein properties.
Area of Science:
- Biochemistry
- Molecular Biology
- Biophysics
Background:
- Cyan fluorescent proteins (CFP) utilize a tryptophan66-based chromophore for live cell imaging.
- Unlike other fluorescent proteins, charged states of the CFP chromophore have not been previously documented.
Purpose of the Study:
- To investigate the potential for deprotonation of the CFP chromophore.
- To engineer CFP variants with altered spectral properties through chromophore modification.
Main Methods:
- Studied synthetic CFP chromophores to determine deprotonation characteristics (pKa).
- Engineered the CFP variant mCerulean by introducing basic amino acids near the chromophore.
- Analyzed spectral properties of the engineered variant.
Main Results:
- The indole group of the synthetic CFP chromophore can be deprotonated with a pKa of 12.4.
- An engineered mCerulean variant with a Val61Lys substitution exhibited green emission.
- This green emission is attributed to an anionic state of the tryptophan-based chromophore.
Conclusions:
- Provides the first strong evidence for an anionic charged state of tryptophan-based chromophores in fluorescent proteins.
- Demonstrates that modulating the protonation state of Trp66 offers a novel method for controlling fluorescent protein spectral properties.
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