Spectral characteristics of the red fluorescent proteins that change the fluorescent spectra with time

Abstract

The spectral characteristics of three monomeric fluorescent proteins - fluorescent timers (FT), created from ancestor protein mCherry were investigated. The main peculiarity of FT is their ability to change in time the fluorescence from blue to red. Obtained FT forms exhibit fast (F), medium (M), and slow (S) blue-to-red chromophore maturation rates. Fluorescent transition times were found to be inversed to temperature. At 37⁰C, the blue fluorescence maxima are observed at 0.25; 1.2, and 9.8 hours for purified FFT, MFT, and SFT, respectively. The half-maxima of the red fluorescence is reached at 7.1; 3.9 and 28 hours, respectively. All FT have excitation and fluorescent maxima for blue forms at 403 and 583 nm, and for red forms - at 446 and 606 nm, respectively. Fluorescence intensities of all studied proteins were constant at рH 4.5 - 7.5 with pK_a near 3.0 for blue and 4.1 - 4.7 for red FT. Molar extinction coefficients were 3400 - 4900 M^-1cm^-1, quantum yields were 0.30-0.41 for blue FT. These values were higher for red forms and altered from 75300 to 84200 M^-1cm^-1 for molar extinction of FFT and SFT; quantum yields of red FT were from 0.05 to 0.09. Fluorescent properties of the investigated FT variants create an opportunity to research some processes with different time characteristics. These FT can be used also for creating protein pairs including green fluorescent proteins for inductive energy transport from blue to green and from green to red forms. It can enlarge the possibility for multicolor fluorescent intracellular detections.