Fluorescence of the Retinal Chromophore in Microbial and Animal Rhodopsins

Abstract

Fluorescence of the vast majority of natural opsin-based photoactive proteins is extremely low, in accordance with their functions that depend on efficient transduction of absorbed light energy. However, several recently proposed classes of engineered rhodopsins with enhanced fluorescence, along with the discovery of a new natural highly fluorescent rhodopsin, NeoR, opened a way to exploit these transmembrane proteins as fluorescent sensors and draw more attention to studies on this untypical rhodopsin property. Here, we review the available data on the fluorescence of the retinal chromophore in microbial and animal rhodopsins and their photocycle intermediates, as well as different isomers of the protonated retinal Schiff base in various solvents and the gas phase.

Rational Design of Far-Red Archaerhodopsin-3-Based Fluorescent Genetically Encoded Voltage Indicators: from Elucidation of the Fluorescence Mechanism in Archers to Novel Red-Shifted Variants

“…For proteorhodopsin and bR, counterion protonation was shown to decrease the efficiency of PSB photoisomerization. , Apparently, neutralization of a negative charge in the NH region is an important condition that allowed the formation of bright fluorescent Archers. It is also worth mentioning here that the available experimental data, which are compiled and analyzed in our very recent review on fluorescent properties of both microbial and animal rhodopsins, suggest that this statement is much more general and goes far beyond the Archers studied here.…”

“…We used the principles formulated above to perform the rational design of new red-shifted bright Arch GEVIs. We chose to optimize red-shifting of λ max not only due to practical importance of red-shifted variants for biomedical applications but also because a clear trend between λ abs and fluorescence quantum yield was observed for microbial and animal rhodopsins (see, e.g., a review). According to the previous studies on electrostatic spectral tuning in rhodopsins (see, e.g., refs , and ), a spectral shift can be achieved by introducing, removing, or displacing/reorienting charged or polar residues.…”