Venus_A206 Dimers Behave Coherently at Room Temperature

Area of Science:

• Cell biology
• Biophysics
• Spectroscopy

Background:

• Fluorescent proteins (FPs) are vital tools in cell biology for genetically tagging proteins in living cells.
• Förster's resonance energy transfer (FRET) measurements using FP-tagged proteins study protein interactions and distances.
• FRET assumes weak coupling between fluorophores, limiting energy transfer interpretations.

Purpose of the Study:

• To investigate the possibility of excitonic coupling between fluorescent proteins at physiological temperatures.
• To determine if fluorescent proteins can exhibit strong coupling, deviating from the weak coupling assumption of FRET.
• To explore the implications of slower FP dephasing times on energy transfer mechanisms.

Main Methods:

• Distinguished FRET from excitonic coupling by monitoring spectral changes during fluorophore dimerization.
• Utilized circular dichroism spectroscopy to detect Davydov splitting in Venus_A206 FP dimers.
• Employed photon antibunching and fluorescence correlation spectroscopy to confirm single-photon emitter behavior in Venus_A206 homodimers.

Main Results:

• Observed Davydov splitting in the yellow FP Venus_A206 upon dimerization, indicating strong excitonic coupling.
• Confirmed that two fluorophores in a Venus_A206 homodimer function as a single-photon emitter.
• Demonstrated that excitonic coupling between Venus_A206 fluorophores can occur under physiological conditions.

Conclusions:

• Excitonic coupling is a viable mechanism for energy transfer between fluorescent proteins at physiological temperatures.
• The study challenges the long-held assumption of weak coupling in FP-based energy transfer measurements.
• Findings suggest that fluorescent proteins may be evolutionarily adapted for stronger coupling than previously thought.