We investigated the donor effects (mCerulean3 versus mTurquoise2.1) on the spectroscopy and dynamics of mCerulean3-linker-mCitrine constructs using integrated fluorescence spectroscopy methods. Here, mCerulean3 (a cyan fluorescent protein) and mCitrine (a yellow fluorescent protein) act as Förster resonance energy transfer (FRET) pair, separated by flexible linker region. We hypothesize that the construct with mTurquoise2.1 would have many advantages as a donor, which include a higher FRET efficiency as compared with the mCerulean3 due to the enhanced spectral overlap with mCitrine. To test this hypothesis, we used steady-state spectroscopy, time-resolved fluorescence, and fluorescence correlation spectroscopy of both mCerulean3-linker-mCitrine and mTurquoise2.1-linker-mCitrine to investigate the donor effect on the FRET efficiency and translational diffusion as a means for developing a rational design for hetero-FRET constructs for environmental sensing.
KEYWORDS: Fluorescence resonance energy transfer, Energy transfer, Energy efficiency, Time resolved spectroscopy, Anisotropy, Environmental sensing, Sensors, Spectroscopy
Förster resonance energy transfer (FRET) is considered as a molecular ruler to quantify protein-protein interactions and structural conformation in a wide range of biomolecules in both controlled environments and in living cells. Here, we have employed integrated fluorescence spectroscopy methods to characterize the energy transfer efficiency and donor-acceptor distance for novel genetically engineered mCerulean3–linker– mCitrine environmental sensors. Based on the amino acids sequences of the linker region, these sensors can be sensitive to either macromolecular crowding or the ionic strength of the surrounding environment. These hetero-FRET sensors also enable us to develop new spectroscopic approaches for quantifying the energy transfer efficiency and the donor-acceptor distance as a means of elucidating the underlying mechanisms for environmental sensing. Ensemble averaging approaches using time-resolved fluorescence and time-resolved fluorescence polarization anisotropy of G12 sensor are highlighted. Our findings in control environments so far are currently being used for complementary studies in living cells.
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