The heterogeneous cellular environment influences a myriad of biological processes. For example, macromolecular crowding affects biochemical reactions, protein-protein interactions, and protein folding. Additionally, the structure-function relationship of biomolecules and enzymatic activities are sensitive to the surrounding ionic strength. In this contribution, we highlight our recent studies on a family of donor–linker– acceptor constructs, which were designed for mapping the macromolecular crowding and ionic strength in living cells. Integrated ultrafast laser spectroscopy methods have been employed to quantify the Förster resonance energy transfer (FRET) and the donor-acceptor distance as a measure of the sensitivity of these constructs to environmental changes. The donor-acceptor FRET pairs are intrinsically fluorescent cyan and yellow proteins, respectively, that can be genetically encoded in living cells. The sensitivity of these constructs to environmental biomimetic crowding and ionic strength was investigated as a function of the sequence and charge of the linker regions, as well as the identity of the donor protein. Integrating noninvasive, quantitative laser-induced fluorescence methods with FRET, as a molecular ruler, provides a powerful tool for cellular studies towards mapping out macromolecular crowding and ionic strength in living cells. Our results are key for the development of rational design strategies for engineering enhanced noninvasive biosensors with better environmental sensitivities. The same sensors were used as a model system for developing new experimental approaches for protein-protein interaction and FRET studies. Importantly, these diagnostic molecular and analytical tools set the stage for understanding the correlation between these environmental factors and cellular functions.
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.
Foerster (or fluorescence) resonance energy transfer (FRET) is a powerful tool for investigating protein-protein interactions, in both living cells and in controlled environments. A typical hetero-FRET pair consists of a donor and acceptor tethered together with a linker. The corresponding energy transfer efficiency of a hetero-FRET pair probe depends upon the donor-acceptor distance, relative dipole orientation, and spectral overlap. Because of the sensitivity of the energy transfer efficiency on the donor-acceptor distance, FRET is often referred to as a “molecular ruler”. Time-resolved fluorescence approach for measuring the excited-state lifetime of the donor and acceptor emissions is one of the most reliable approaches for quantitative assessment of the energy transfer efficiency in hetero-FRET pairs. In this contribution, we provide an analytical kinetics model that describes the excited-state depopulation of a FRET probe as a means to predicts the time-resolved fluorescence profile as a function of excitation and detection wavelengths. In addition, we used this developed kinetics model to simulate the time-dependence of the excited-state population of both the donor and acceptor. These results should serve as a guide for our ongoing studies of newly developed hetero-FRET sensors (mCerulean3–linker–mCitrine) that are designed specifically for in vivo studies of macromolecular crowding. The same model is applicable to other FRET pairs with the careful consideration of their steady-state spectroscopy and the experimental design for wavelength- dependence of the fluorescence lifetime measurements.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.